Transactions of the Geological Society, 1st series, vol. 2/On the Strata lying over the Chalk

by Thomas Webster

VII. On the Freshwater Formations in the Isle of Wight, with some Observations on the Strata over the Chalk in the South-east part of England.

By Thomas Webster, Member of the Geological Society.

INTRODUCTION.

AMONG the geological researches which have lately been made in various parts of the globe, none have been more interesting than those of M. M. Cuvier and Brongniart in the environs of Paris.

These naturalists have described a series of mineral strata differing in many respects from all that were formerly known, and particularly distinguished by their numerous and singular organic remains. The animals whose exuviæ had hitherto been more commonly noticed in regularly stratified rocks were the inhabitants of an ocean: but many of the Parisian fossils belonged to freshwater lakes and marshes, thus developing new and unsuspected agents in the forming of mineral beds.

The strata described by the French naturalists are deposited in a cavity in the chalk stratum which extends through a considerable part of the north of France. The bottom of this hollow is extremely irregular; and before it was covered by the materials now found in it, must have presented partial cavities and projections, the latter appearing as so many islands piercing through the other strata; and it is an important observation that there is no correspondence between the irregular form of the bottom and that of the present surface of the country.

Although the number of distinct beds or layers in this basin is very considerable, yet the authors of the memoir have reduced them to eleven principal classes.

1. Chalk.
2. Plastic clay.
3. Coarse limestone and sandstone.
4. Silicious limestone.
5. Gypsum and marl, containing bones of animals, forming the lower freshwater formation.
6. Marles of marine origin.
7. Sand and sandstone without shells.
8. The superior marine sandstone.
9. Buhr or millstone formation without shells, and argillaceous sand.
10. The upper freshwater formation, comprehending marles and buhrs with freshwater shells.
11. Alluvium or earth of transportation, both ancient and modern, analogous to our gravel, &c. comprehending rounded pebbles, pudding stones, argillaceous marles and peat moss.

Of these the three first above the chalk are of marine origin, and they cover the whole of the bottom of the basin.

The gypsum and accompanying marles they imagine to have been formed chiefly in fresh water, from the fossils contained in them.

The next series of marles and sandstones containing only marine shells, shows the sea to have again covered the last formed strata.

Lastly, the upper freshwater formation demonstrates this place to have been a second time converted into a lake.

Such are the leading features of these remarkable strata.

It is the object of the present paper to describe a similar series of formations; from which it will appear that the circumstances which gave rise to the alteration of marine and freshwater strata were subject at distant places to the same general laws, and were therefore extensive in operation: conclusions in themselves not uninteresting, and tending to throw some light on the later revolutions which our planet has undergone.

Sir Henry Englefield was the first who observed a range of chalk hills running from east to west across the middle of the Isle of Wight, and inclined at an angle of from 60° to 80°. An account of these strata appeared in the Transactions of the Linnean Society, 1802;^[1] but circumstances having prevented him from prosecuting these geological researches in person, at his request in the summer of 1811 I examined the connexion of the vertical strata of the Isle of Wight with those on each side which are horizontal, and also the continuation of this range to the west on the opposite shore of Dorsetshire.

The general result of this enquiry will be best understood from the following section across the Isle of Wight from north to south; see plate 11^{[errata 1]}, fig. 1.

Plate 11, Fig. 1.

The inclined strata A, B, C, D, E, compose a range of hills that divides the island into two parts, extending from the Needles at the west end of the island to the Culver cliff at the east: at which places may be seen vertical sections at right angles to the direction of the range.

The stratum marked A, is chalk with flints,^[2] which at the north side is in nearly vertical layers, the inclination becoming gradually less and less towards the south side, where they dip about 60°.

2. is chalk without flints.
3. chalk marl.
4. calcareous sand-stone, with subordinate beds of limestone and chert.
5. bluish-black marl.
6. ferruginous sand and sand-stone, with potters' clay, slate clay, argillaceous limestone, wood-coal, &c. The part of this stratum in the middle ranges of hills inclines only a few degrees, extending to the south side of the island, where it is horizontal. It is to be remarked, that towards this side of the island there is a higher range of hills H, composed of horizontal strata which correspond exactly with a part of those of the highly inclined series of the middle range, not only in their nature, but in their order of superposition; thus irresistibly forcing upon us the conclusion, that they belonged to the same formation, and that they had probably at some period been continuous.

The strata G, to the north of these already mentioned, consist of a numerous alternating series in a vertical position, and are composed chiefly of sand and clay. These may be seen to great advantage in Alum bay, where they form cliffs about 200 feet in height.

The whole of the most northern part of the island, I, consists of nearly horizontal strata, which come up abruptly against those that are vertical, but are slightly curved at their junction with the latter. These, however, proved to be entirely different in their mineralogical characters and in the fossils which they contained, from the strata that I have described on the north side of the island, under the chalk.

Several of them were composed of a calcareous rock, either of a loose or compact texture; and an attentive consideration of this section, together with those of the opposite coasts of Dorsetshire, Hampshire, and Sussex, convinced me that the date of their origin was posterior to that of the chalk.

No distinct limestone stratum had been hitherto observed above any part of the chalk in this country, although it was well known that such were frequent in France. That this is the real position of the limestones near Paris could not be doubted, since the chalk is always reached in sinking to great depths. But the geognostic place of the strata on the north side of the Isle of Wight, was more difficult to ascertain; and it was only from many combined considerations that I was led to the conclusion, that they might be found to agree with some of those lately described by Cuvier and Brongniart, as contained in the basin of Paris.

These considerations were the following:

The chalk of England, although it appears upon the surface only in detached hills and patches, is actually continuous through considerable tracts of country, where it exists at great depths, as is now ascertained by numerous wells and other sinkings. In the order of position, which the strata of the chalk itself, and those which lie above and below it, bear severally to one another, there has been observed in distant places a remarkable agreement. And although occasional varieties may be noticed, in consequence of the defect or redundancy of any one stratum, yet the law of the Wernerian school seems to hold good; viz. that the order of the beds is never inverted.

This agreement renders it extremely probable that the corresponding strata, found in different parts of the same country, arose from the same cause, and at the same time; and favours the idea, that many of these, although now broken and unconnected, were originally continuous.

A part of the series which I deduced from observations made in the south-eastern part of England, is as follows, beginning with the uppermost.

1. Alluvium, consisting of gravel, loam, sand, &c. and forming the surface or soil.
2. Sand seen chiefly in the neighbourhood of Bagshot.
3. Blue clay, with septaria and marine fossils, commonly called the London clay.
4. Sand, plastic clay, &c.
5. Chalk with flints.
6. Chalk without flints.
7. Chalkmarl, including what is called the grey chalk.
8. Sandstone with green earth and mica, cemented together by calcareous matter, and containing subordinate beds of limestone and chert. This includes the firestone of Ryegate, and Kentish rag.
9. Blueish black marl.
10. Sand and sandstone, highly ferruginous, containing subordinate beds of clay, fullers earth, shale, bituminous wood, and limestone. This stratum forms the wealds of Kent and Sussex.
11. A series of strata of shelly limestone, known by the name of the Purbeck stone, alternating with shale and marle. Some of the fossils of these strata strongly resemble freshwater shells: they appear to be the Cyclostoma, Planorbis, &c.
12. Clay with gypsum.
13. Portland oolite.

14. Clay with limestone and bituminous shale, containing the Kimeridge coal.^[3]

The strata of Alum bay, now seen in a vertical position, must have been originally quite horizontal, or nearly so. For it is not only extremely improbable that beds of such materials should have been formed^{[errata 2]} in any other manner, but a circumstance which I noticed in Alum bay renders certain the original position of the sand and clay strata. In one of the vertical beds, consisting of loose sand, are several layers of flints, extending from the bottom to the top of the cliff; these flints have been rounded by attrition; are from one inch to eight inches in diameter, and appear to have belonged to the chalk. Now it is inconceivable that these flint pebbles should have been originally deposited in their present position; and they distinctly point out the original horizontality of this series. There are no signs of partial disturbance in the several beds, and it appears therefore that the whole have^{[errata 3]} been moved together, either by elevation or subsidence into the vertical situation.

The strata of chalk have evidently suffered a change of position at the same time with the clay and sand; and since the vertical beds of Alum bay, G, are next to the stratum of flinty chalk, which, according to the regular order of superposition, is known to have been the uppermost of the chalk series, it follows, that they are of posterior formation. Moreover, the most northern of these vertical beds is a blue clay, agreeing with the London clay, a bed which always lies over the chalk.

The chalk of the middle hills of the Isle of Wight dipping to the north, and that of the South Downs dipping to the south, it was an obvious inference that it might pass under the channel called the Solent, thus forming a basin. This idea was rendered still more probable on finding that the bottom of this channel consisted mostly of the London clay, which stratum is found under Portsmouth, whence it may be traced eastward, forming the lowermost bed next the sea all along the shore of Sussex to Pagham and Bognor, and westward to Stubbington cliffs, and along the coast of Hampshire to Hordwell and High cliffs. In all its characters and fossils, this bed was found to agree with the blue clay which lies over the chalk, in the counties of Kent, Surrey, Middlesex, Essex, &c. and with the most northerly of the vertical beds of Alum bay.^[4] Besides, the chalk itself lies at no great depth from the surface in all that part of Sussex south of the South Downs, and is even found on the shore at low water-mark at Middleton, two miles east of Bognor.

It appears, therefore, that between the vertical chalk-hills of the Isle of Wight and the South Downs there is a basin or hollow, occasioned by the disturbance of the whole mass of strata from below the chalk to the London clay, inclusive: and also that this disturbance took place at a period subsequent to the deposition of the last-mentioned stratum, since it is amongst those which have suffered a change of position.

From this it will be readily admitted, that all the beds situated within this basin lie above the London clay, and are posterior to it. Of this description are the horizontal beds of the most northerly part of the Isle of Wight; and since they come almost into contact

with the vertical beds without suffering any considerable change in their dip, it should seem that they have been deposited on the sides of this basin subsequently to the disturbance of the strata already spoken of.

The above conclusions are confirmed by other circumstances.

These horizontal beds have no agreement with any of those beneath the chalk, nor indeed with any others yet observed in Great Britain; their mineralogical characters, and their fossils, are peculiar and distinctive. The calcareous beds contain numerous petrifactions^{[errata 4]} of freshwater shells, and in others are found marine fossils agreeing with those described by Lamarck in the strata of the Paris basin. But fortunately, the inspection of specimens from the basin of Paris enabled me no longer to depend upon conjecture only as to the similarity of these formations. They had been given by M. Brongniart himself, in illustration of his memoir, to the Count de Bournon, who had deposited them in the museum of the Geological Society. The agreement of the strata of the two basins, not only with respect to the external characters of the calcaire d'eau douce, but also to its fossils, was thus rendered evident: and these specimens, so well authenticated, added one more proof (if more could be wanting) of the utility of such collections, and of the advantages to be derived from a liberal communication between men of science.

It is unnecessary to inform the Society that this circumstance produced another visit to the Isle of Wight and its vicinity, for the purpose of examining more particularly its basin, and the remains of its ancient lake. From this, compared with my former survey, I was enabled to add to the British strata the following, of later formation than the London clay.

1. A calcareous stratum, containing only freshwater shells.
2. Greenish marl, with marine shells.

3. Marl with freshwater shells.
4. Dark blue clay without shells.

These must be placed between the alluvium and the London clay, of the former list.

In the subsequent pages I shall describe more minutely the form of the basin of the Isle of Wight; and also that of a similar basin on which London is placed. I shall enumerate the strata and principal organic remains contained in each, and conclude by pointing out such circumstances of agreement or difference as I have been able to observe between them and the Paris basin.

II. Extent of the Isle of Wight Basin.

In tracing the margin of the cavity in which these horizontal depositions of the Isle of Wight are found, I shall begin with the south side.

The middle range of chalk hills in this island, together with the other highly inclined strata of Alum bay, form part of the ancient border. If we sail west from the Needles in the Isle of Wight, to Handfast point in Dorsetshire, we shall find that this vertical chalk range again makes its appearance in that coast, and may be traced thence through Corfe Castle to some distance beyond Lulworth; and from the correspondence in the line of direction of the Isle of Wight hills with those of Dorsetshire, and the general agreement in the position and nature of the strata, (the section of the Isle of Purbeck corresponding nearly to that of the Isle of Wight,) it appears extremely probable that at some former period these places were united.

The clay however over the chalk, and part of the chalk itself, in Dorsetshire, is horizontal, differing in this respect from their position in Alum bay. There must, therefore, have been some twist in the chalk stratum, a remarkable instance of which I discovered at the other end of the chalk range beyond Lulworth.^[5]

Since I shall have a future opportunity of making some remarks on the very singular stratification of these places, I shall only at present observe, that the highly inclined chalk from the Culver cliffs at the east end of the Isle of Wight to White Nose, in Dorsetshire, 5 miles west of Lulworth, formed the southern side of this depression in the chalk stratum. The north side of it may be traced in that range of hills called the South Downs, extending from Beechy Head, in Sussex, to Dorchester, in Dorsetshire. The strata of which these hills are composed, dip generally from 15° to 5° to the south; the inclination varying in different places. The south side of the basin therefore must have been extremely steep, while the slope of the north side was very gentle. The closing of this basin at the west is obscure, and cannot be distinctly traced; but the east is now entirely open, the sea passing through it.

III. Extent of the London Basin.

This extensive basin, like that of the Isle of Wight, is probably owing to a depression in the chalk stratum.

Its south side is formed by a long line of chalk hills, including those of Kent, Surrey, and Hampshire, called the North Downs, extending through Basingstoke to some distance beyond Highclere Hill, in Berkshire. Its western extremity is much contracted, and seems to lie somewhere in the vicinity of Hungerford. Its north-western side is formed by the chalk hills of Wiltshire, Berkshire, Oxfordshire, Buckinghamshire and Hertfordshire. The most northern part of this boundary has not yet been well determined. On the east it is open to the sea, the coasts of Essex, Suffolk and Norfolk, being sections of the strata deposited in it.

The dip of the chalk of the North Downs from Dover to Guildford is from 15° to 10°, but in the narrow ridge of chalk called the Hog's-back, extending from Guildford to Farnham, the dip is very considerable being above 45°.^[6] On the dip of the other sides I have had no opportunity of making any observations.

The depth of the chalk below the surface at London must be very considerable, since though wells have been sunk several hundred feet it has never been reached; but at a few miles south of the metropolis the chalk is frequently come to.

IV. Description of the Strata composing and contained in the Isle of Wight and London Basins; with a comparison between them and those in the Basin of Paris.

The authors of the French memoir, in order to obtain their general section, have collected the sections of various places; and by comparing them together have developed those alternations of marine and freshwater deposits, which are analogous to those we are now considering. I shall follow nearly the same method; but for greater simplicity I shall divide the formations composing our basins into

1. Chalk formation.^[7]
2. The lowest marine formation over the shell, including the plastic clay and sand, together with London clay.
3. The lowest freshwater formation.
4. The upper marine formation.
5. The upper-freshwater formation.
6. Alluvium.

Fortunately the complete series of these alternations may be seen at one place in the Isle of Wight, which leaves us no room to doubt their superposition; and when their characters have been studied in this spot, it is more easy to become acquainted with them in other places.

§ 1. Chalk Formation.

The south-east coast of England and that of the Isle of Wight afford us many excellent opportunities of examining the chalk. In numerous natural sections formed by cliffs, as well as in chalk pits, I have observed it as distinguished into at least three strata, each of which has peculiar and distinctive characters.

The lower stratum is more or less argillaceous, and constitutes what is called the chalk marl. Together with the other strata it frequently forms cliffs of considerable height, and though differing little from them in colour is easily distinguished by its constantly shivering with the frost, which always pulverizes a mass of it when exposed to the air for a few months; whereas the others resist the weather in a much greater degree, and are often even employed as a material for building.

This chalk marl is never quite so white as chalk, having generally a tinge of yellow, and sometimes of grey and brown. It also contains nodules and beds of a more indurated marl, which is usually called the grey chalk from its dark colour, which varies from a light to a dark grey and brownish grey. Like all argillaceous limestones it possesses in a considerable degree the property of setting under water when calcined and made into mortar; and it has been used with great success for this purpose in building the London Docks. The part easily reducible to the pulverulent state by the moisture and frost is a most valuable manure when employed judiciously in certain soils. This stratum contains no flints.

The middle and upper strata consist of chalk of extreme whiteness and purity, and are chiefly distinguished from each other by the upper one containing layers of flint nodules which do not occur in the lower. The chalk without flints is most frequently somewhat harder than that with flints, and hence they are sometimes distinguished as the hard and soft chalk; but from some observations which I have made in Dorsetshire, it will appear that the hardness, or degree of induration, does not always mark a particular bed, the flint chalk being in some places much harder than that without flints in others.

On the subject of the nodules and laminæ of flint in the upper chalk, the observations of Sir Henry Englefield have thrown great light, and will be mentioned in his intended work on the Isle of Wight.

The several beds of these chalk strata, which vary in thickness from a few inches to several feet, are frequently separated from each other not only by layers of flint nodules but frequently also by a marl containing a considerable proportion of clay, and this substance also sometimes fills up the diagonal fissures which cross the strata. The workmen take advantage of this circumstance in quarrying the chalk.

The description given by M. M. Cuvier and Brongniart of the chalk of France appears to agree generally with that detailed above. They mention nodules of a harder chalk as occurring in layers in a softer. They observe that Werner has enumerated grey and brown among the colours belonging to chalk: and that in a great part of Champagne the chalk contains no flint,^[8] but it does not appear whether these varieties of chalk are on the continent confined to particular strata.

M. M. Cuvier and Brongniart remark that the chalk which forms the bottom of the Parisian basin, appears to have been consolidated before the deposition of the clay which covers it: a circumstance which they inferred from there being no transition of these into each other. A breccia is described as occupying the lower part of the basin at Meudon, composed of water-worn fragments of solid chalk cemented by a paste of clay, and situated between the chalk and the plastic clay. This circumstance, together with the irregular form of the bottom of their basin, seems to indicate a considerable action of water upon its surface, so as to render it now difficult to ascertain what might have been the last depositions of the chalk formation, or those which immediately succeeded it.

Some appearances shew that a similar action had taken place on the original surface of our chalk. Many very interesting sections may be seen in the County of Kent, where the chalk being at no great depth, its junction with the strata over it may be very conveniently studied. At Woolwich, on the top of the chalk, and between it and the superimposed sand, there are a number of flint nodules heaped on each other, which have evidently been displaced from their original matrix. In the numerous chalk pits, and where the roads are cut through the chalk along the south side of the Thames, as at Rochester, Gravesend, North Fleet, Greenhithe, &c. the junction of the chalk with the sand and gravel is remarkable for the deep indentations in the surface of the former, which upon examination I ascertained to be the sections of long furrows and of wells; these were apparently occasioned by the powerful action of water prior to the deposition of the sand and gravel which now fills up these hollows: the same may be seen still better at Purfleet.

The present surface of the chalk stratum is also frequently covered by water-worn pieces of chalk and flint imbedded in clay or alluvial deposits.

The cliffs between Brighton and Rottendean are of a singular character, and merit a particular description. The shore consists of the solid chalk, which is seen running out to a considerable distance into the sea, and dipping a few degrees to the south. This stratum forms six or seven feet of the lower part of the vertical cliff; and on that are placed several layers of loose flints, evidently rounded by attrition and piled on one another. Over this is an irregular bed consisting of pieces of chalk and smaller pieces of flints, both of which have undergone the same process; and the interstices are filled up with clay and loose chalk or marl: over this is another layer of pebbles, and again clay and chalk and fragments of flints; and these follow in succession, but very irregularly, to the top of the cliffs which is at least seventy or eighty feet in height. These materials are in general quite loose, being simply heaped or laid on each other; but sometimes masses of it are cemented together by stalactitical matter, and when the cliff falls, form blocks of great size and hardness.

It is impossible to see this cliff without immediately perceiving that it does not owe its existence to original stratification; but that it is simply the section of an immense heap of fragments of chalk and flints mixed with clay and sand, the whole of which has at some distant period been subjected to the action of water; and that it has been thus deposited upon the solid chalk stratum which is now seen below it.

In tracing this vast collection of water-worn materials, we find that it forms a considerable hill behind the town, and that it joins to the side of the range of hills called the South Downs.

In Alum bay in the Isle of Wight, however, the stratum immediately next to the flinty chalk, and consequently deposited upon it, consists of a white chalk marl without flints. Its nature is sufficiently shewn by its pulverizing with the frost; and the rains wash it down, so that its situation is marked by a deep hollow. There is some appearance here therefore of a transition of the last portions of the chalk into the clay which succeeded it; and, the usual rounded flint pebbles over the chalk and the other signs of disturbance being there wanting, it is possible that we have in that place the original succession of depositions. In many parts of Sussex also, south of the South Downs, as at Emsworth, Lavant, Siddlesham, South and North Bersted, Middleton, &c. I found pits of a marle without flints, and which is evidently over the chalk. The same marl is also to be found in Dorsetshire west of Corfe Castle. I have not however heard of its existence in the London basin.

The agreement of the fossils of our chalk with that of France has been already pointed out by Mr. Parkinson in his Memoir “on some of the Strata in the neighbourhood of London,” in the first volume of the Transactions of this Society. In the following lists I have been favoured by his assistance in the endeavour to appropriate the fossils to their peculiar beds.

In the Chalk with Flints.
Asteriæ	resembling
	Pentagonaster semilunatus
	──────	regularis
	Pentaceros lentiginosus
	Stella lumbricalis, lacertosa, corpore spherico.
Echini	of the following families.
	Cidaris	$\left.{\begin{matrix}\ \\\ \\\ \\\ \\\ \end{matrix}}\right\}$ several species.
	Cassis,
	Spatangus,
	Fibula,
	Conulus,
Spines of the foregoing: particularly those resembling the belemnites as described by Mr. Parkinson.
Serpulæ, particularly the serpula of Mr. Parkinson's organic remains, vol. 3. pl. 7. fig. 11.
Cardium.
Spondylus.
Ostrea, several species.

Pecten, several species.

Chama?

Terebratula, many species.

A longitudinal transversely rugose ostrea-form bivalve of a fibrous structure.

Fragments of mother fibrous shell of a large size, of an unknown genus. See Hark. Organic Rem. pL 5. fig. 3.

Alcyonia, sponges, and numerous unknown zoophytes.

A ramose madrepore.

Several species of minute encrini, figured by Mr. Parkinson.

In the Chalk without Flints.

Echini: several of the same families as those in the chalk with flints. Many of them, however, particularly the Cassides, differing much in their forms from the above.

Spines of echini: and particularly those described by M. Braard as resembling the belemnite.

Patella.

Trochus.

Serpulæ, several species.

Belemnites.

Lima?

Fish, too much mutilated to ascertain the genus.

Palates, scales, vertebræ and teeth of fish.

Cancri.

In the Chalk Marl.^[9]

Ammonites: the contour of the spiral varying from the circular to the long-elliptical.

Scaphites: a new genus by Mr. Parkinson. See his Organic Remains, vol. 3.

Turrellites, three species.

Trochus.

Madreporæ.

It has been remarked by the French naturalists that in their chalk there is not any univalve shell with a simple and regular spire. In the chalk of this country, univalves, as the trochus, do sometimes occur. They may probably however be rather the fossils of the green sand below the chalk, which have been enveloped in some of the depositions of the chalk formation, or in the chalk marl, for they are frequently accompanied by green earth.

The following Fossils are found in the Chalk in the Environs of Paris

Belemnites	Perhaps two species: they appear to be different from those in the compact limestone.
Lenticulites rotulata.
Lituolites nautiloidea.
————— difformis.
Pinna	It is not certain that the large fragments of 12 millimetres in thickness and of a fibrous texture, which are found in the chalk belong to this genus. M. Defrance has portions of a hinge which indicate a different genus. Cuv. p. 11.
Mytilus	very different from those of the calcaire grossier.
Cardium?
Ostrea vesicularis.
———— deltoidea.
Pecten	M. Defrance has observed 2 species.
Crania	It was adherent and differing in that from known species.
Perna?
Terebratula, many species.
Spirorbis.
Serpula.
Ananchites ovatus	The shell is changed into calcareous spar, and the internal part is converted into flint.
Spatangus Cor anguinum Kl.
Porpites.
Caryophyllia
Millepora	These are often in the state of brown oxide of iron.
Alcyonia.
Shark's teeth.

§ 2. Lowest Marine Formation over the Chalk.

The clay and sand cliffs of Alum bay afford one of the most interesting natural sections that can well be imagined. They exhibit the actual state of the strata immediately over the chalk before any change took place in the position of the latter. For, although the beds of which they are composed are quite vertical, yet, from the nature and variety of their composition, from the great regularity and numerous alternations of the layers, and the other circumstances which have been already mentioned, no one who has viewed them with attention can doubt, that they have suffered no change except that of having been moved with the chalk from the horizontal to the vertical position.

The whole of these strata have evidently been formed at the bottom of an ocean, from the nature of the fossils contained in them, which, although entirely different from those of the chalk, are yet all of marine origin.

The chalk, A, which forms the side of Alum bay, (Plate 11. Fig. 2.) is somewhat harder than usual, and the flints are shivered, so as to come to pieces on being taken out.^[10]

Plate 11, Fig. 2.

Next to the chalk, on the north, stands the bed of chalk marl a, which has been already mentioned.

To this succeeds a thick bed of clay, b, of a dark red colour, often streaked or mottled with yellow and white; towards the south side is a thin layer of greenish-grey sand. This is divided by a bed of yellowish white sand, c, from a very thick bed of dark blue clay, d, which contains much green earth; and also nodules of a dark coloured limestone, in which I found a few fossil shells: this bed, however, I am inclined to think, is not continuous for a great extent, as in a part of the cliff farther inland and in the line of its direction, it had almost disappeared.

Next follows a vast succession of beds of sand of different colours, which, though not distinctly separable from each other, yet may be considered as divided into the following:

e,	Greenish yellow sand.
f,	Yellow sand with ferruginous masses.
g,	Greenish sand, like e.
h,	Yellow, white, and greenish sand.
i,	Whitish sand, with thin stripes of clay.
k,	White and yellow sand.
l,	Light green sand.
m,	Ferruginous sand stone.
n,	Yellow sand with a few red stripes.
	Next to this, and in the middle of the bay, is a very numerous succession of beds, which contain a large proportion of pipe-clay of various colours, white, yellow, grey, and blackish. These alternate with beautifully coloured sands. The clay is sometimes in beds several feet in thickness, without any admixture, and sometimes in laminæ not a quarter of an inch thick with sand between them. They are generally as follows:
o,	Blackish clay with stripes of white sand.
p,	Sand intensely yellow.
q,	Very white sand. In the middle of this there is a layer of small siliceous nodules, quite white, easily frangible, and of an earthy texture; they are water-worn, and seem to have been derived from decomposed flints.
r,	Sand of a crimson colour.
s,	Pipe clay with sand stripes. Here it runs into the sea, and may be traced across the beach.
t,	Yellow sand with some crimson.
u,	Pipe clay, white and black, with stripes of sand. In the middle there are three beds of a sort of wood coal, the vegetable origin of which is distinctly pointed out by the

	fruits and branches still to be observed in it. It sometimes splits into irregular layers in the direction of the bed, and the cross fracture is dull and earthy. It burns with difficulty, and with very little Same, giving out a sulphurous smell.
v,	Yellow and white sand, with crimson and grey stripes.
w,	Five beds of coal similar to that above-mentioned, each a foot thick.
x,	Whitish sand and brownish pipe clay.
y,	Whitish sand with stripes of deep yellow.
z,	Several layers of large water-worn black flint pebbles, imbedded in deep yellow sand.
B,	A stratum of blackish clay, with much green earth and septaria. In this green earth are a prodigious number of fossil shells, but in a very fragile state. They correspond exactly with those of Stubbington and Hordwell.

A stream of water from the adjoining hill has worn a deep channel through the stratum, and affords a path down to the bay.

To the north of this, the strata C consist of yellowish sand; and it is not easy to see what is really the position of those beds which lie immediately next to the blue clay, but they appear to dip about 45° to the north; and the sand D lying on them is nearly horizontal.

The north side of Alum bay is bounded by a hill called Headen, about 400 feet high, considerably loftier than the vertical cliffs, and composed of the same part of that series of horizontal strata of which the north side of the island consists. In this hill only do we distinctly see the alternation, I have mentioned of marine and fresh water deposits. It is in a state of constant ruin, and by its section affords lofty vertical cliffs, where its strata may be examined with the utmost facility.

The last mentioned sand is the lowest stratum there visible. It is above 30 feet in thickness, beautifully white, and in it several pits are annually dug, from which the manufactories are supplied with their materials for the best flint glass. This sand may be traced round the foot of the hill on the north side, and forms the bottom of Totland and Colwell bays, dipping gradually to the north.

Over it lies a horizontal bed of black clay E which contains fossil shells, and sometimes selenite.

Upon reviewing the whole of this lower marine series of strata in Alum bay, and comparing it with other sections of the strata immediately over the chalk, we shall find it useful, for the present at least, to separate it into two great divisions: 1. Sand and plastic clay, 2d. London clay. From the irregularities in the beds in the few places where there are good sections, these divisions however can as yet scarcely be considered as distinctly determined. Thus much is certain, that the plastic clay and sand is always below and never above the London clay. Other sub-divisions may be introduced when future observations shall shew them to be sufficiently important.

1. Sand and Plastic Clay. From the constant and abundant supply of water which is found on boring through the London clay, and from the accounts of the proprietors of the numerous pits of plastic clay in Dorsetshire, the sand must be considered as the most extensive and continuous formation, and the clay as filling up basins or hollows in it. Hence, as may naturally be expected, we find each of these substances in different places in immediate contact with the chalk. In the Isle of Wight clay is next to it, but in the numerous sections on the banks of the Thames, sand is the lowest, or the clay is wanting.

The beds of plastic clay in the Isle of Wight are of unusual extent and thickness. They extend quite across the island in a vertical position, keeping parallel to the chalk, and appearing again at White-cliff bay on the east end, where they are however much concealed by grassy slopes.

All along the north side of the range of chalk hills which extends from Handfast-point through Corfe Castle, there is an extensive stratum of pipe clay in a horizontal position. It contains a bed of coal so exactly resembling that of Alum bay, that this circumstance, added to the quality of the clay and its geognostic position, is sufficient to identify it.

I have been favoured by Alexander Jaffray, Esq. with the following section of the clay pits of Norden, near Corfe.

Sand on the top	10	feet
Blackish brown clay	14
Wood coal	3
Refuse clay	5
Fine white potter's clay	6
Dark brown clay	2
Fine white potter's clay	6$\scriptstyle {\frac {1}{2}}$
	───
	46$\scriptstyle {\frac {1}{2}}$

The same stratum of clay, though not of equal quality, may be traced in the hills near Poole; and is found in many parts of that extensive tract called the trough of Poole.

Potter's clay, white, yellow, or greyish white, similar to that in the Isle of Wight, is also frequently found in the London basin: some of it is of considerable fineness, as on the east bank of the river Medway, near Rochester.

The plastic clay is frequently of a deep red colour, or red and white mottled, as in Alum bay: a similar red clay is dug near Portsmouth and other places along the South Downs. It also appears at Reading.

In the Isle of Wight basin, both in Dorsetshire and Alum bay, beds of iron stone and ferruginous sand occur connected with this clay, and generally lying over it. Considerable rocks of it are seen about Studland, and the Druidical monument, called the Agglestone;^{[errata 5]} near that place is a huge block of this bed.

A stratum of sand, containing green particles, frequently occurs near the chalk. It is seen in Alum bay without fossils; at Reading it is found containing oyster shells. This green sand is easily distinguished from that below the chalk, as it is never indurated.

2. London or Blue Clay. The stratum which has received this dedenomination is found immediately under the gravelly soil on which the metropolis is situated. Of all the strata over the chalk in this country, it is of the greatest extent and thickness: and the number, beauty, and variety of the organic fossils which it contains, renders it the most interesting and the most easily recognizable.

It consists generally of a blackish clay, sometimes very tough, at other places mixed with green earth and sand, or with calcareous matter.

It contains also numerous flat spheroidal nodules of indurated marl, or argillaceous limestone, which lie in regular horizontal layers, at unequal distances, generally from four to ten feet apart. These nodules are well known by the name of Ludus Helmontii, or Septaria, from their being divided across by partitions or veins of calcareous spar, which are generally double. In their cavities are frequently found crystals of calcareous spar and of sulphat of barytes. The septaria are surrounded by crusts which contain a smaller proportion of carbonat of lime than the central part. They often include organic remains.

Besides the clay, marl, sand, and carbonat of lime, of which the main body of this stratum consists, several other substances are dispersed through it in smaller quantities. Of these the chief is sulphuret of iron, which is frequently the mineralizing matter both of the vegetable and animal remains included in the blue clay.

Selenite is also very abundant; and sulphat of iron frequently effloresces when the clay is exposed to the air, from the decomposition of the pyrites contained in it. Phosphat of iron is also sometimes found.

On account of these salts, the water which is contained in, or which passes through this stratum, is not fit for domestic purposes.^[11] Wells are therefore generally sunk entirely through it to the sand below.

In the country round London, this sand which belongs to the plastic clay, is the great reservoir of water, which generally bursts out with great violence when broken into.

Sulphat of magnesia has long been known in the springs at Epsom, which has given its name to this salt. Its origin however does not appear to have been clearly ascertained, although from its situation it may be supposed to belong to some of the beds above the chalk. I derive from Mr. Tennant the information, that the London clay abounds in Epsom salts. The bricks of old buildings in London, after fine dry weather, are covered with an efflorescence of this salt. This may be seen in the walls of the Temple.

In the Isle of Wight, as well as the London basin, this stratum occupies the same situation, and does not appear to differ materially in each of these places. In Alum bay it is seen forming the most northerly of the vertical strata. On the opposite shore of the Solent it occurs in a horizontal position. Sections of it are formed by the cliffs between Lymington and Poole. Of these, Hordwell cliff, below Christchurch, is well known, on account of its fossils, which are found in a very perfect state. They have been collected and very accurately described by Mr. Brander and Dr. Solander.

At Stubbington, a few miles west of Portsmouth, the same stratum of blue clay with much green earth is visible, in a low cliff, with the same fossils as at Alum bay and Hordwell: the strata being horizontal. The fossils here, as at Alum bay, though numerous, are in a very fragile state; minute nummulites are extremely abundant.

Portsmouth is built upon this stratum, and several deep wells sunk there afford us much information. James Hay, Esq. F.L.S. kindly furnished me with the following account of the sinkings at that place.

“1. Vegetable mould.

2. Yellow loam, of which excellent bricks are made.

3. Yellow gravel, composed of rounded siliceous pebbles and sand, from 4 ft. 6 in. to 10 feet thick. In some places, towards the bottom, the sand abounds; and, generally, within a few feet of the blue clay, is very fine, and in many places is of a greenish colour. In the yellow gravel are found many organic remains, siliceous, and all rounded by attrition. In a few instances singular bones have been discovered.

4. An immense bed of blue clay, which in many places at the surface is mixed with sand strata. At the depth of 30 feet it is traversed by a thin stratum of white pebbles. Many wells are dug to this stratum, which contains water, but of a hard quality. At the depth of 60 feet another similar stratum is found, containing water also, and of a softer quality. No wells had been sunk lower than this last stratum, until within 15 years ago, when a well was dug in the Dock Yard, to the depth of 202 feet. Excellent water was then found. Another well was dug about a quarter of a mile north from Portsmouth, where water of a good quality was obtained at a depth of 126 feet from the surface. Two years ago a well was sunk in the town of Portsmouth, to the depth of 266 feet, without getting through the blue clay, and they left of without finding water. This is the greatest depth they have gone to in this place. The fossils dug up from these wells agree exactly with those found in other parts of the same stratum.”

I traced this blue clay west of Portsmouth by Emsworth and Chichester harbours to Brackelsham; and thence round Selsey Bill to Pagham harbour.

At Bognor it assumes a new character; instead of a blue clay, we find here a number of rocks, now appearing as detached masses in the sea, though evidently forming portions of a stratum once continuous. The lowest part of these rocks is a dark grey limestone, or perhaps rather a sandstone, containing much calcareous matter, enclosing many fossils belonging to the blue clay. The upper part is a siliceous sandstone. Bognor rocks resemble much the nodules and beds of limestone that are found in the blue clay in Alum bay, and no doubt are owing to the great abundance of calcareous matter in this part of the bed.

The Barns rocks between Selsea and Bognor, the Houndgate and Street rocks on the west, and Mixen rocks to the south, of Selsea, are portions of the same bed; and I found similar but smaller masses at Stubbington.

From this place to Brighton the shore is quite flat, and the chalk lies at no great depth.

The coast at Brighton has been already mentioned. At Rottendean the cliff towards the sea consists of chalk, and this continues to Newhaven. At this place a series of beds above the chalk occurs, forming to the west of the river a hill, the greatest part of which is now destroyed by the action of the sea. At this place the chalk is about 50 feet in height, and is covered immediately by a bed of sand 20 feet thick. Over this are thin strata of yellow marl and clay, containing a coal much resembling that of Corfe and Alum bay. H. Warburton, Esq. Secretary to the Geological Society, who first noticed and pointed out to me these interesting strata, found impressions of leaves in the marl which exactly resemble those engraved in one of the plates of the Essay on the Mineralogy of the Environs of Paris: and I have since recognised among the specimens brought from that place, a fruit of one of the palm tribe, with the vegetable fibres quite distinct. Shells belonging to the Genera Cerithium, Cytherea and Ostrea, together with pyritous casts of the same, also occur.

With this coal are found thin masses of gypsum both selenitous and fibrous; and over all is a thick bed of blue clay with marine fossils, which are different from those usually found in the London clay.

It was here that I found the singular substance which the experiments of Dr. Wollaston ascertained to be a new mineral, a subsulphat of alumine. It lies immediately upon the chalk, and fills up a hollow in it. About a mile on the east side of Newhaven the chalk cliffs rise again to an equal height and continue to Cuxhaven, where there is a similar interruption, and thence extend to Beachy Head, increasing regularly in altitude, and forming tremendous precipices of several hundred feet in height.^[12] The chalk here is covered only by a thin layer of sand and gravel.

Turning round this promontory, the lower chalk and chalk marl are seen at the bottom of the cliff and rising to the north-east, where they soon take place of the chalk, forming a mouldering slope at South Sea houses; they there give place to the green sand, which continues some way, then dips, and is covered by a flat beach extending many miles along Pevensey bay. It is almost needless to observe that the cliffs from Rottendean to Beachy head are oblique vertical sections of the South Downs, and have been formed by the action of the sea.

On entering the London basin at the south side from the sea, after passing the chalk cliffs at North Foreland and Margate, the blue clay makes its first appearance at Reculver; and at Swale cliff and Whitstable it is again seen.

But the Isle of Sheppey, consisting entirely of this stratum, and whose lofty cliffs on the north side furnish very extensive sections, affords the best opportunity for studying it.

Of this island, the northern half consists of a range of hills, of above 200 feet in height. These are cut down vertically by the action of the sea, which occasions the cliffs continually to fall: whole acres of land sometimes coming down at once; in consequence of which, the island must in a course even of a few centuries have suffered considerable diminution. The southern half of the island is entirely alluvial, being only a few feet above the level of the sea; and owes its origin to the gradual filling up of the channel which separates the Isle of Sheppey from the rest of Kent. It now consists of flat marsh land, which has been gained from the sea by embankments.

A little to the north of the eastern point, called Shellness, from the great number of recent shells that lie on the shore, a low cliff exhibits the section of the alluvial soil, which consists of clay and gravel. At Warden the high cliff begins on the east, and extends towards Sheerness on the west above six miles in length.

The clay of which these cliffs are composed is in all respects similar to that which has been cut through in the neighbourhood of London at Highgate, and at the Regent's Park; and this place is particularly known on account of its furnishing abundance of the septaria, from which that excellent material for building under water and for stucco is made, known by the name of Parker's cement. These nodular concretions of stone-marl are separated from the clay by the action of the sea, and are collected upon the beach, and exported to various places, where they are calcined and ground.

At Sheerness a well was sunk 380 feet through the blue clay, an account of which is in the Philosophical Transactions: and from this we may obtain an idea of the thickness of the stratum: for to this must be added 200 feet, the height of the cliffs, making in all 550 feet.

The cliffs of Sheppey have long been celebrated for the numerous organic remains found in them, a list of which, added by Mr. Jacob to his Plantæ Favershamienses, is well known. But a much more extensive collection has since been formed by Mr. Francis Crow, of Feversham, who has enriched it by the addition of above 700 different species of fossil fruits, berries, and ligneous seed vessels.

This ingenious and indefatigable collector has also lately ascertained a number of fossil bodies found among them to be the excrescences produced by insects on the branches of various trees; and I have been since favoured by him with a portion of the jaw of a crocodile found in Sheppey; a fossil extremely interesting, since it is the only instance yet observed of the bones of this animal having been found in the London clay.

Almost the whole of the vegetable and animal remains are entirely impregnated with sulphuret of iron, and the vestiges of shells are chiefly casts in this substance. The quantity of fragments of pyritous branches^[13] and fruits is very great.

Among the pyritous casts of shells I found one that much resembled the lymneus, and another the planorbis, but too imperfect to decide the species. It is proper however to mention, that in a late number of the Journal de Physique, in a paper on freshwater shells by M. Braarde, mention is made of three freshwater shells from Sheppey, the lymneus, melania, and nerita.

These shells however, which are very few in number, do not prove the existence of a freshwater formation in this place similar to those of the basins of Paris and of the Isle of Wight: being found among the remains of vegetable and of marine animals, we may suppose that they were carried down together with the branches of trees and fruits by the numerous streams and rivers that must have flowed into this gulph.

Most of the best preserved organic remains are enclosed in the septaria: in these the shells often retain their original pearly lustre. The nautili are particularly fine.

Boughton hill, between Feversham and Canterbury, consists of the London clay. Still nearer to Feversham fossil shells are found, which are entirely siliceous. They lie loose in a thin bed of greenish siliceous sand that occupies a situation lower than the blue clay, and are separated from the chalk by a thick bed of yellow sand. Mr. Crow has collected here the strombus pes pelecani, a murex, a species of cucullea, and several other bivalves.

One of the most interesting sections above the chalk is to be seen at Woolwich, near the banks of the Thames. At this place the junction of the chalk with the strata over it is plainly to be seen. Over the chalk is a stratum about 30 feet thick of very fine white sand; and towards the top there is a thin bed of clay. Next succeeds a stratum of about 10 or 12 feet, composed wholly of flint pebbles, which have been worn by water into their present forms, and lie in the utmost confusion piled on each other, having a vast number of fossil shells lodged in the interstices.

The whole has the appearance of having been at some period a heap washed up on the sea shore, similar to our modern beaches. The shells are entirely whitened, and having lost their animal matter, are extremely brittle: their species however may be in general ascertained, although very few are to be found entire. They have been already described by Mr. Parkinson.

The bottom of this stratum of pebbles is now about 30 feet above the level of the sea. Over this is a layer of sand with some ferruginous masses, and then several thin strata of clay alternating with sand. In this clay are vast numbers of bivalves, locked into each other so close that this must doubtless have been their original bed. Other beds of sand succeed, and on the top there is a stratum of dark blue clay a few feet thick.

This bed, which is frequently referred to by Woodward in his history of fossils, has also excited the particular attention of Mr. Parkinson: but its fossils differ so much from those usually found in the London clay, that it is not easy to decide upon the place to which it ought to be referred; particularly since it is not even covered by a bed that can be identified with the London clay. Bivalves, resembling those of Woolwich, have been brought up in digging wells at other places on the banks of the Thames, but I am not aware that cerithia and the other fossils of this stratum have been so found. This bed is known to extend for a considerable distance on the south of the Thames, in the counties of Kent and Surrey. It is found at Bexley and Plumstead, at which latter place a thin stratum of minute fossil shells was laid open a few years ago, but which now appears to be lost.

At Bromley, which is not far above the chalk, vast quantities of oysters are found imbedded in a calcareous cement and forming, together with rounded pebbles, a sort of rock. It has been observed that these oysters are found adhering to the pebbles, indicating the formation of the latter previous to the growth of the former.

Woodward, in his catalogue, frequently mentions a bed of stone as occurring at Stifford in Essex, and containing fossil shells which agree with those at Woolwich and Bexley. In a late visit which I made to that part of the country for the purpose of ascertaining this fact, I was not fortunate enough to procure specimens of the rock. It is not indeed new to be seen where it is described by that author, being probably concealed by cultivated ground: but I learned that a stone did exist under the soil, which the labourers frequently came to in ditching, and I mention this in the hope that some one residing in that neighbourhood may examine into this matter.

It is said that thin strata of a calcareous rock are found in sinking wells through the London clay; but of this I have not seen any well authenticated specimens. The circumstance however is far from being improbable.

The extensive works now carrying on in the neighbourhood of the metropolis, as the cutting the hill at Highgate, the tunnel lately carried under the Thames at Rotherhithe, one under Hyde Park, the canal now forming in the Regent's Park, and several others of a similar kind, have thrown great light upon the nature of the London clay and its fossils, and furnish daily opportunities for observation highly useful to all those who are interested in the examination of our upper strata.

At Highgate-hill the beds consist of

1. Vegetable mould.
2. Several feet of loose gravel and highly ferruginous masses of sandstone.
3. Yellow clay.
4. Blue clay, in which great numbers of marine shells and parts of fish were found.

On the south side of the River Thames near Rotherhide, a shaft sunk for a tunnel proposed to be carried under the Thames, exhibited the following strata.

Feet
6	9	Vegetable mould.
9	0	Brown clay.
26	8	Gravel with water.
3	0	Blue clay.
5	1	Loom.
3	9	Blue slay with bivalve shells.
7	6	Gravel stones imbedded in a calcareous rock.
4	6	Light blue soil with pyrites.
1	9	Green sand.
8	4	Leafy clay.

The bottom of the shaft was 30 feet under the bed of the river Thames. The unfortunate failure of the project, from the river bursting in before they had completed a drift, is well known.

At Reading there are several pits dug for the purpose of procuring brick clay, some of which reach to the chalk; an account of the strata at this place is given us by Dr. Brewer in the Phil. Trans. 1800.

Immediately incumbent on the chalk is a stratum 2 feet thick of green sand containing numerous oyster shells. Many of these are entire, having both their valves united; but the animal matter being entirely gone, and the shell not having undergone the process of petrifaction, they are white and extremely brittle, and separate into laminæ. Fishes teeth are also found with them. Over this is a bed 8 feet thick of a bluish rough clay, then fuller's earth 21/2 feet, and fine white sand 7 feet. Next is a stiff red clay, probably the plastic clay, of which tiles are made. This is much thicker than any of the other beds; and over is the alluvial soil. These strata are known to extend for several miles with little variation.

At Brentford, on the borders of the Thames, about 6 miles from London, many important discoveries have been made in the grounds of Mr. Trimmer; an account of which has lately been read before the Royal Society. Here the chalk lies at a great depth, as they have dug 200 feet through the blue clay without coming to it. Immediately upon this clay are a few feet of sand and gravel with water; over that from 1 to 9 feet of calcareous loam; then sandy gravel 7 feet, and lastly calcareous loam or common brick earth 9 feet. In the blue clay were found the usual fossils of this stratum, being entirely marine. The three beds just over it contained a vast collection of the bones of elephants, both African and Indian, of the hippopotamus, the horns and jaws of oxen, the horns of deer, and both land and freshwater shells.

Richmond Park is on this stratum, and Woodward frequently refers to this place in his History of Fossils; but there are no longer any sections to be seen there, the spot being covered by buildings.

Wells of 70 feet deep have been dug at Harrow-on-the-hill; and several in London between 200 and 300 feet deep. At other places on rising grounds the depth of this stratum is much greater. In digging a well for Lord Spencer, at Wimbledon, they were obliged to go 530 feet deep before they got through it to the sand which contained water. At Primrose-hill, near Hampstead, a well was dug some years ago to the depth of 500 feet without success.

This considerable formation may not only be traced on the north side of Kent and Surrey, but almost the whole counties of Middlesex and Essex are composed of it. At South-end, and Leigh in Essex, there are good sections of it. But not having an opportunity of visiting the coast farther to the north, I am unable to speak with certainty respecting the various strata to be observed there.

The cliffs at Walton and Harwich, in Essex, have been best described. From various accounts the lowest part consists of blue clay, the fossils of which agree generally with those of Hordwell, Sheppey, &c. This clay is covered by deep beds of gravel, sand and marl, containing not only great quantities of fossil shells but also the remains of land animals.

From the confused manner in which these shells and pebbles lie, as described by Mr. Dale in his history of Harwich, there can be no doubt but that the strata containing them are frequently alluvial; though in the cases where he describes them as lying in patches of particular genera, we may suppose that portions of the original strata remain undisturbed.

Many of these latter fossil shells must belong to some of our latest strata: they are described as scarcely mineralized, very friable, and of a dead white colour.

The counties of Suffolk and Norfolk have been little explored, and still present a wide field for research. They will I have no doubt amply reward those members of the Society who have opportunities of examining them.

I shall now proceed to point out those particulars in which I have observed the marine formation which we have been examining to be analogous to some of the strata in the basin of Paris.

The plastic clay of the Paris basin is described as sometimes consisting of two beds separated by a bed of sand, The lower bed is properly the plastic clay. It is unctuous, tenacious, containing some siliceous but no calcareous matter; and absolutely refractory in the fire when it has not too great a portion of iron. It varies much in colour, being very white, grey, yellow, grey mixed with red, and almost pure red. This clay is employed, according to its quality, in making coarse or fine pottery and porcelain.

The corresponding beds of clay in this country agree well with this description. The clays of Dorsetshire are extremely pure, and are much employed in the potteries of Staffordshire and other parts of England. In Alum bay we see clays of all the colours just described. Some of them appear very promising, so much so that the late Mr. Wedgewood had pits opened there; but although extremely refractory, they were found upon trial not to burn sufficiently white for the purposes required. The deep red clays we have seen are very common in many parts of the country over the chalk.

No fossil shells have been found in this bed of clay in the French basin, nor in the clay pits of Dorsetshire; nor are there any in the pure clays of Alum bay.

The uppermost bed of potters' clay in France is sandy, blackish, and contains sometimes fossil shells of the genera cytherea and turritella, and the sand is often coloured red or bluish grey.

In the stratum of blue clay, next to the deep red clay that adjoins the chalk of Alum bay, there are septaria with fossil shells, among which I found cytheræ and turritellæ; the rest were too much mutilated. Hence it would appear, that no fossil organic bodies are disseminated through the pure plastic clays of either basins, but that they are to be found in such beds of this clay as are impure.

A species of imperfect coal also occurs in the lower strata of the Paris basin, and is probably analogous to that of Corfe, Alum bay, and Newhaven.

The French sands are of a great variety of colours. The sands of Alum bay may correspond to that between their chalk and the plastic clay, which is described as very pure, though often coloured red or blueish grey. It is refractory, and often in very large grains.

In the lower marine formation of the Paris basin, the most remarkable and best characterized stratum is that of the coarse shelly limestone or calcaire grossier. This is generally separated from the chalk by the clay and the sand just described; or, when that is wanting, it rests immediately upon the chalk. It is sometimes, also, separated from the clay by a bed of sand, more or less thick, in which no shells have been found.

The description given by the French of this calcareous formation is extremely precise, and corresponds to its importance. From this it appears to be composed of alternate beds of limestone, more or less hard, of argillaceous marl, of laminated clay, in very thin beds, and of calcareous marl. These are of great extent, and preserve constantly the same order of superposition, although all the beds are not continuous. Each bed is also characterized by its peculiar fossils. The lower are often more sandy than calcareous, and when solid they fall to pieces on exposure to the air. They frequently contain a considerable quantity of green earth, and this is found only in the lower beds, a circumstance which they have pointed out as particularly indicative of them.

The lowest bed is also particularly distinguished by the vast number of fossil shells contained in it; the greatest part of which are more unlike the recent shells than those of the superior beds. The fossil shells of this bed are often well preserved, and are easily detached from their matrix; and many of them have still their original pearly lustre.

The middle beds also inclose a great many shells; one of them is called the green bank, from its colour. It often contains impressions of leaves and stalks of land vegetables, mixed with cerithia, ampullariæ, and other marine fossils.

The next bed of calcaire grossier has less variety of fossil shells than those just mentioned, but the cerithia are very abundant in it: and towards the top there is a thin bed, containing a prodigious quantity of corbulæ, long shaped, and striated. Above these are the marls, both calcareous and argillaceous; with calcareous sand, sometimes agglutinated, and which contains hornstone with horizontal zones.

The uppermost beds of this system have much fewer shells; and these are generally altogether wanting at the top.

In passing over in review all the strata which we know above the chalk in England, there does not appear to be any one that can be considered as exactly corresponding to this considerable and well marked stratum in the basin of Paris; and in instituting a comparison between the English and French strata, were we to require a perfect agreement in all the beds, we should here totally fail.

Yet although we cannot point out a calcareous rock precisely similar, and possessing the same importance of character, I think a sufficient number of circumstances may be shewn to justify our considering the greatest part of the materials of this formation as existing in the English basin, but differently modified.

For this purpose I shall consider the organic remains, which the French have observed to belong peculiarly to these beds, as very important.

The general correspondence between the fossil shells of Grignon and those of Hampshire, has been already pointed out by several able naturalists, and in particular lately by Mr. Parkinson. I should therefore scarcely have considered it necessary to state here what is already so well known, had I not been enabled during my late journey to the Isle of Wight, to add several not hitherto observed, and which bring the agreement still closer; and since organic remains furnish one of the best methods of identifying strata, or rather perhaps formations, it may at present be interesting to bring into one view the most characteristic fossils that have been observed in this formation in England.

The liberal assistance of Mr. Parkinson has enabled me not only to give the scientific names of Lamarck to the several fossil shells which I found, but also to add the corresponding Linnean names, by which they are chiefly known in this country. This however could not be done in every case, since many of the fossils of Lamarck were not known to former naturalists.

Organic remains in the Lower Marine formation above the Chalk in England.

Names given by Lamarck.	Linnean names.	Place where they have been found.
Astriotæ	Astroitæ	Sheppey
Calyptrea trochiformis	Trochus apertus, Brander	Hordwell, Bognor, Woolwich, Plumstead
Conus	Conus	Hordwell, Stubbington
Cyprea pediculus	Cyprea pediculus	Stubbington, Highgate
Terebellum convolutum	Bulla sopita, Brand.	Hordwell
Oliva	Voluta	Alum-bay
Voluta spinosa	Strombus spinosus	Alum-bay
──── musicalis	──── luctator	Hordwell
──── bicorona	──── ambiguus	Hordwell
──── crenulata	Murex suspensus	Hordwell, Alum-bay
	Voluta ampullaria	Brentford, Alum-bay
Buccinum undatum		Alum-bay
Harpa		Brentford
Cassis carinata	Buccinum nodosum, Bran.	Stubbington, Highgate
Rostellaria macroptera	Strombus amplus	Hordwell, Highgate
Murex tripterus	Murex tripetrus	Hordwell
──── tricarinatus	──── asper	Hordwell
──── tubifer	──── pungens	Hordwell
	──── contrarius
	──── whirls the right way
Fusus longævus	──── longævus	Hordwell
──── clavellatus	──── deformis	Hordwell
──── rugosus	──── porrectus	Hordwell
Pyrula nexilis	──── nexilis	Hordwell
Pleurotoma?		Alum-bay
Cerithium gigantum	Murex	Stubbington
Cerithium, another variety, but too mutilated to ascertain the species	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$Murex	Sheppey
Trochus agglutinans	Trochus umbilicaris, Bran.	Stubbington, Hordwell
──── monilifer	──── nodolusus	Hardwell
Solarium caniculatum or	Turbo, tab. 1. fig. 7 & 8. Brander	Hordwell
Delphinula?	Turbo, tab. 1. fig. 7. Brand.	Hordwell
Turritella terebellata	Turbo terebra	Hordwell, Stubbington, Alum-bay, Selsea
──── imbricatoria	──── editus	Hordwell, Stubbington, Alum-bay, Selsea
──── multisulcata	──── vagus	Hordwell, Stubbington, Alum-bay, Selsea
Ampullaria patula	Helix mutabilis	Hordwell, Stubbington, Bognor
Dentalium elephantinum	Dentalium elephantinum	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,}$Hordwell, Sussex
───── entalis	───── entalis
───── dentalis	───── dentalis
───── striatulum	───── striatulum
Serpula	Serpula	Hordwell; Bognor, Sheppey
Nautilus imperialis		Sheppey, Highgate, Brentford
───── pompilius		Sheppey, South-end, Highgate, Brentford
───── centralis		Richmond
Lenticulina rotulata		Stubbington
Nummulites lævigata		Brackelsham in Selsea
Pinna, 2 species	Pinna	Bognor
Mytilus modiola	Mytilus	Bognor, Highgate
Pectunculus pulvinatus	Arca glycemeris	Bognor, Stubbington, Essex
Cardium porulosum	Cardium porolusum	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right\}\,}$ Hordwell
───── asperulum	───── asperulum
───── obliquum	───── obliquum
Crassatellata lamellosa	Tellina sulcata	Hordwell
Venericardia planicosta		Stubbington, Selsea
Capsa rugosa	Venus deflorata	Pagham
Chama lamellosa	Chama squamosa	Hordwell
───── calarata		Hordwell
───── sulcata		Hordwell, Stubbington, Alum-bay
Ostrea edulis	Ostrea edulis	Bognor, Selsea, Essex
Pyrus bulbiformis		Hordwell, Stubbington; Alum-bay
Caryophillia	Turbinated Madrepores	Sheppey
Teredo navalis	Teredo navalis	Stubbington, Portsmouth, Sheppey, Bognor, Highgate
Jaw of Crocodile		Sheppey
Testudo or Turtle		Sheppey
Various Fish, but too mutilated to ascertain the species		Sheppey
Fish teeth, supposed by some to belong to the shark		Sheppey, Stubbington, Highgate
Molar teeth of fish, called Bufonites		Sheppey
Palatum Scopuli and other palates of fish		Selsea, Sheppey
Tongue of fish of the genus Raia		Sheppey
Tail of the String Ray		Highgate
Scales of fish		Sheppey
Vertebræ of various species of fish		Sussex, Sheppey, Highgate
Cancer, above 20 species of Crabs		Sheppey
———— Gammarus or Lobster		Sheppey
———— Crangon or Prawn		Sheppey
Wood, often pierced by the Teredo navalis &c filled with pyrites or calacareous spar		Portsmouth, Sheppey, Highgate
Fruits, branches, excrescences, ligneous seed vessels and berries impregnated with pyrites		Sheppey, Emsworth in Sussex

Although nearly 600 species of fossil shells have been described by M. Lamarck as belonging to the calcaire grossier, Messrs. Cuvier and Brongniart have selected the following as particularly characteristic of the several beds.

Lower beds

Nummulites lævigata	Cerithium giganteum
————— scabra	Lucina lamellosa
————— numismalis	Cardium porulosum
————— &c.	Voluta cithara
Madrepora	Crassatella lamellosa
Astraæ	Turitella multisulcata
Caryophyllia	Ostrea Flabellula
Fungites	——— Cymbula
Middle beds
Cardita avicularia	Citheria nitidula
Orbitolites plana	———— elegans
Turritella imbricata	Miliolites
Terebellum convolutum	Cerithium?
Culyptræa trochiformis	Articulate bodies
Pectunculus pulvinatus	resembling vegetables
Upper beds
Miliolites	Cerithium lapidum
Cardium lima or obliquum	———— petricolum
Lucina saxomrum	Corbula anatina?
Ampullaria spirata	———— striata
Cerithium tuberculatum	Impressions of leaves
———— mutabile

Messrs. Cuvier and Brongniart remark that the nummulites are found only in the lowest beds of the calcaire grossier, to which belongs also the cerithium giganteum. I am enabled by the information of Mr. Holloway, who pointed out to me these fossils at Bracklesham in Selsea, and also in Stubbington cliff near Portsmouth, to add this very strong circumstance of agreement with the French strata.

It is impossible not to be struck with the identity of the fossil shells of the sandy beds of Liancourt with those of Stubbington.

At the former of these places are found:

Nummulites lenticularia

———— lævigata

Turritella terebellata

———— imbricataria

Crassatella sulcata

Venericardia planicosta

Sharks' teeth

The whole of which are to be found at Stubbington.

These beds of Liancourt contain also masses of sandy limestone filled with chlorite: and Stubbington is remarkable for the quantity of green earth which it contains.

A circumstance is mentioned by the French authors which appears to point out a remarkable era in the history of these strata. They observe, that in the beds of the lower marine formation, and particularly in those of Liancourt, natural wells of considerable size are sometimes found, filled with ferruginous and sandy clay and water-worn siliceous pebbles. These wells do not pierce through all the beds of the calcaire grossier; but begin at the same level, and are covered and closed by the uppermost beds: shewing that they were formed after the period of the formation of the lowest, and before that of the upper beds; which points out a very long interval, and the action of violent causes during this time.

It may be remarked, that this is exactly the period to which we must look for the subversion of the strata of the Isle of Wight, and the formation of its basin. If therefore the deposition of the upper beds of the calcaire grossier was general, and extended to this part of the globe, it must be placed at the lowest part of the Isle of Wight basin, and probably therefore at an inaccessible depth.

The rocks of Bognor and Selsea appear to be the most easily referable to some of the beds of the calcaire grossier of France. The correspondence in their geognostic situation, in the nature of their materials, and in the fossils which they contain, sufficiently justify the supposition.

Although in general the beds of the calcaire grossier maintain a regularity remarkable and distinctly to be traced, yet that is not always the case, the quarries of Saillancourt being cited as an exception to this rule: all the beds are there united, and nearly of

the same quality, which appears to be owing to calcareous spar cementing the parts together. In our blue clay there is a considerable quantity of carbonat of lime in a sparry state, as is evident from the septaria.

The middle and upper beds of the French calcaire grossier frequently contain a sandstone, with marine shells which agree, though not entirely, with those of the calcaire. This sandstone is sometimes white and friable, and sometimes shining and almost translucent. The shells are frequently white, calcareous, and well preserved, though sometimes broken and mixed with pebbles.

The sandstone which forms the uppermost beds of the rocks of Bognor, already described, do not differ much from this description. It contains some fossil shells of the same species, though not in such numbers as the lower beds; and some of those in the lower beds, as the pinnæ, are not met with in the upper beds; the shells also are frequently whitened.

By connecting all the above circumstances it would appear, that if we could suppose a blending or mixture between the French plastic clay, which is blackish and contains organic bodies, and the lower beds of the calcaire grossier with its green earth and fossils, we should have a compound agreeing sufficiently near with our London clay under all its varieties; with this difference, that that of the French basin would have a greater proportion of calcareous, and ours of argillaceous matter. We may therefore fairly infer that they belong to the same epoch. But with respect to the upper beds of the calcaire grossier of France, no strata have yet been discovered in this country that correspond to them. Whether any such ever existed, and whether any traces yet remain, may perhaps prove a fit subject for future enquiry.

§ 3. Lower Freshwater Formation.

This formation is to be seen most distinctly in the section of the hill called Headen, which forms the northern boundary of Alum bay, in the Isle of Wight. It appears there in a series of beds of sandy calcareous and argillaceous marls; sometimes with more or less of a brownish coaly matter. Some of them appear to consist almost wholly of the fragments of freshwater shells, many of which are however sufficiently entire to ascertain their species. These are the lymneus, planorbis and cyclostoma, and perhaps the helix; with a bivalve resembling the freshwater mytilus.

These beds lie immediately upon the black clay that covers the white sand, described in the account of Alum bay. They are extremely irregular, and are not to be traced distinctly from each other for more than about a few hundred yards, the remaining part being so hid by the mouldering slope, that the formation can only be observed in mass. It may be seen however extending round the north side of Headen into Totland bay, where it forms the upper part of the cliff: and at the point called Warden-ledge, it is found in a more uniform and indurated state. Here, when the clay upon which it rests gives way from the rain and frost, large masses of it fall down, which are employed for the purposes of building, though the stone is not of a good quality. Pursuing it farther into Colwell bay, it dips to the north, and is soon lost; nor is it to be seen any more on that side of Yarmouth. At the bottom of these beds, and between them and the black clay, there is frequently a layer of two inches or more in thickness of a dark brown coaly matter, much like what is usually found at the bottom of peat bogs, and it appears to be a similar substance that tinges many of the beds.

On a careful examination I was not able to discover any mixture of marine shells in this series of beds. Had they ever existed I think their remains would have been evident, considering how much thicker and stronger marine shells in general are than those of freshwater.

The quantity of shells, and the regularity and extent of the strata in which they are found, are much too considerable to suppose that they could have been carried by rivers or streams into an arm of the sea; and in this case there would also most probably have been a considerable intermixture of marine shells. We are compelled therefore to admit that the spot where they now are, was once occupied by freshwater, in which these animals existed in a living state.

The mutilated condition in which these shells appear, seems to denote that they had not become mineralized sufficiently to preserve their forms, or that the place in which they were accumulated was occasionally subject to agitations.

Freshwater strata occur occasionally in other parts of the west and north coasts of the Isle of Wight, but in such an irregular manner that it is not easy to say to what formation they belong.

Among those at Cowes and Ride there are none that I can completely identify with these beds. But I am at present inclined to think that the same formation exists at these places, though under a character considerably different.

The quarries of Binstead, near Ride, were formerly of great celebrity, and furnished the materials for many ancient edifices, both civil and religious, in the Isle of Wight and the counties contiguous to it. They are now very little worked; but their extent may be traced by the broken ground where they have been filled in.

The section of the strata is as follows, beginning at the bottom.

		Feet.
1.	Blue clay	depth unknown
2.	Sand	50	0
3.	A Siliceous limestone called rag	0	6
4.	Sand	0	8
5.	Siliceous limestone	0	6
6.	White shell-marl	0	10
7.	Siliceous limestone	1	6
8.	Limestone composed of the fragments of freshwater shells	1	6
9.	Ditto, the fragments more apparent	2	0
10.	Ditto, the fragments still larger	4	0
11.	Ditto, fragments still coarser	2	0
12.	Blue Clay, in which are many large and loose masses which appear to belong to the upper Freshwater formation.

At East Cowes Lord Henry Seymour had the goodness to point out to me a quarry which he had caused to be opened in his grounds, the strata of which were almost exactly the same as those of Binstead. The rag from this quarry his Lordship had employed in the construction of his mansion; and also in the fine wall which he has built to keep off the encroachments of the sea.

In the strata of East Cowes the casts of the shells are frequently entire, and appear to belong to the genus Cyclostoma Lam.

The fragment stone of Binstead, when examined with a magnifier, has a very singular appearance. In some specimens the fragments themselves remain, though in a sparry state; but in general the substance of the shell has disappeared, leaving a cavity where it formerly existed; so that in fact, instead of being fragments cemented together by calcareous spar, the stone consists of the hollow moulds of fragments held together by that matter. It would seem as if the shells themselves had been gradually absorbed into the substance of the cement.

The whole of the north shore of the Isle of Wight has been for ages in a state of constant ruin by the action of the sea and the sliding down of the soil. It is difficult therefore to find any past of the strata in their original situation; on this account freshwater and marine shells are frequently found together in confusion. I have however observed some places where they occur in alternate layers.^[14]

The cerithia, cyclades, cytheræa, oysters, and other fossil shells, which are so numerous on the shore near Cowes, are derived from the blue clay of the upper marine formation, which is situated above that which we are now considering, and of which the sloping banks chiefly consist.

That occasional alterations and mixture of marine and freshwater shells should occur, might^{[errata 6]}, a priori, be expected. They would denote either the gradual nature of the change that has taken place in an arm of the sea before it became completely a lake of freshwater, or the occasional irruptions of the ocean at a subsequent period.

These beds may be traced a considerable way eastward of Ride, and I believe as far as Nettlestone, but I have not had an opportunity of ascertaining their precise boundaries. Neither have I been able to learn with certainty that any part of this formation is to be found on the coasts of Hampshire on the opposite side of the Solent; and I do not find it eastward on the Sussex side.

Woodward, however, in his valuable catalogue of fossils, frequently makes mention of freshwater shells in a marly stone from the Hordwell cliffs. It is very probable therefore that traces of this formation may be found there, if this spot were well examined for the purpose.^[15]

Land and river shells have been repeatedly discovered in various parts of England; and often at some depth under beds of sand and gravel. They are then often accompanied by the bones of land animals as those of the elephant, hippopotamus, &c. and may be referred to a very ancient period probably connected with some of these formations. None of them however had as yet been discovered imbedded in a stratum of rock. When they have been found under peat bogs they have been most probably produced in some of the later states of the earth.

It is in this formation, in the Paris basin, that the gypsum beds are placed. Three series of gypseous strata are described: the lowermost consists of thin beds of gypsum, often selenitous, of solid calcareous marls, and foliated argillaceous marls; and they observe, that these are sometimes deposited on the marine shelly calcareous sand, and then they contain marine shells. In these are also beds of white marl, containing a great quantity of freshwater shells of the genera limneus and planorbis. These lower beds, with the white marl, constitute the oldest freshwater formation; and, according to the observations of M. M. Cuvier and Brongniart, appear to have been formed during the passage or change of the Paris basin from the state of a marine bay to that of a freshwater lake. The second mass of beds differs from the above mentioned in the gypsum being thicker, and in the occurrence of a bed of very indurated clay containing fossil fish. The third or uppermost mass is the most important, the beds of gypsum being very thick; it is here alone that the bones of unknown birds and quadrupeds are met with. Freshwater shells are also found in it, though rarely.

Over the gypsum are very thick beds of calcareous and argillaceous marls; one of the latter, which is white and friable, contain silicified trunks of palm trees, and in the former are found many freshwater shells. In this freshwater formation are found neither the meulieres, nor any other flints, except the silex menilites, and the hornstone of the upper gypsum beds.

The total absence of beds of gypsum and of the remains of quadrupeds, in this formation in the Isle of Wight, (at least as far as my observations extend) exhibits a striking proof, that although probably of contemporaneous origin, yet the circumstances accompanying its formation were very different from those under which that of the basin of Paris was produced. The gypsums of Montmartre are well known; and they are considerably different in their appearance from those of England, which belong only to strata far below the chalk. It has been already observed, that selenite is very abundant in our blue clay; but this arises from the decomposition of the pyrites contained in it.

§ 4. Upper Marine Formation.

Over the lower freshwater formation in the Isle of Wight, a stratum occurs, consisting of clay and marl, which contains a vast number of fossil shells wholly marine. Few of these shells agree with the species that have been found in the London clay, and they are also considerably different from them in their state of {hws|preserva|preservation}} preservation; most of them appearing to have undergone but little change, and some are even scarcely to be distinguished from recent shells.

The situation of this bed, distinctly, placed above the vestiges of a freshwater lake, would seem to indicate some great revolution in the relative level of the land and sea, since the time of the marine deposit which we have already considered; and the above circumstances, combined with its position as regards the vertical beds of Alum bay, point out in strong characters a later period.

The spot where this stratum is best examined is Headen, near Alum bay. It there appears half way up the cliff; is about 36 feet thick, and dips a few degrees to the north. It passes from thence all round Totland and Colwell bays.

The substance of the stratum is chiefly marl of a light greenish colour, and the fossil shells are so numerous that they may frequently be gathered by handfulls, and are in general extremely perfect. I did not observe that the several species occupied separate beds, although they were much thicker together in some places than in others, and were then oftener accompanied by rounded nodules of greenish indurated marl. From the delicacy of the shells and their perfect preservation, it is evident that they could not have been brought from great distances, but must have lived near to the spots where they are now found. This greenish marl is separated from the upper freshwater formation only by a bed of sand a few inches in thickness.

In Colwell bay, at a fissure called Bramble's chine, there is in this stratum a very large bank of fossil oyster shells; the greater part of which are locked into each other in the way in which they usually live, and many have their valves united. It is therefore clear that this oyster bed has never suffered a removal. This stratum may be traced, with various interruptions, all round the north side of the Isle of Wight, and may be seen at Cowes, Ride, and Bembridge.

In the enumeration of the various strata in the basin of Paris, our attention is particularly called to a thin bed of bivalve shells covering the upper beds of gypsum and gypseous marls of the lower freshwater formation, the shells of which are placed close, and as it were locked into each other. This bed, though apparently of little importance, is remarkable by its great extent; having been observed over a space of more than 10 leagues in length, and more than 4 in breadth, and always retaining the same situation and thickness. It is still farther distinguished as marking out the beginning of the new series of strata deposited by the sea.

Over this thin bed of bivalves there is one of greenish marl without fossils; and then several alternating beds of argillaceous and other marls and sands, containing marine fossils, shells, and bones of fish. Two beds of oysters are particularly noticed; and it is observed that these must have lived upon the spot where they now are, because they are locked into each other as in their natural beds, with many of their hinges entire. The uppermost beds of marls are however not constant; sometimes, as at Chellis, there is only a thin bed of sand between the green marl and the upper freshwater formation. It is in these marls that the silex menilite is found.

The changes which the surface of the earth has experienced have no doubt destroyed so much of the last depositions in the London as well as in the Isle of Wight basins, that it is impossible to say what the complete series was originally.

Of the existence of this upper marine formation therefore in the London basin, I must speak with diffidence, more particularly since an extensive freshwater formation might never have existed there, and consequently the last marine deposits would be placed immediately upon the lower ones, and would be less easily distinguished, as is frequently the case in the basin of Paris, where we are informed that the sandstone without shells, which is over the marls belonging to this formation, is placed immediately upon the siliceous limestone of the lower marine formation, on the heights to the east of Melun and of Samoineau; the gypsum being wanting there. But as it forms the summits of almost all the bills and plateaux where the gypsum beds are found, they form a separation between the upper and lower marine strata, and render their distinction no longer uncertain. In the counties of Suffolk and Norfolk, there are very extensive beds of marine shells, imbedded chiefly in a ferruginous sand, and lying above the London clay, which have been described under the name of Crag pits. Among the fossils which have been enumerated as belonging to these beds, many agree with those in the upper marine formation in the Paris basin, and others do not appear to differ from the recent shells of the neighbouring seas.

Fossil shells agreeing with the recent occur also in many other parts of the kingdom, now considerably removed from the sea, and are often buried under beds of gravel. These probably belong to the last states of the earth, and might; serve as a clue to unravel geological mysteries.

If we depend upon fossils as a principal means of identifying strata, we shall see great reason to believe that the last of our marine depositions are nearly allied to the upper marine formation of the basin of Paris.

In this stratum in the Isle of Wight I found the following fossils.

Names given by Lamarck.	Linnean names.
Cerithium plicatum	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,}$ Murices
– – – – – lapidum
– – – – – mutabile
– – – – – semicoronatum
– – – – – cinctum
– – – – – turritellatum
– – – – – tricarinatum
Cyclas deltoidea	Venus
Cytherea scutellaria	Venus
Ancilla buccinoides	Voluta
– – – – subulata	Voluta
Ampullaria spirata	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$ Helices
– – – – – depressa?
Murex reticulatus
Bivalve apparently of the genus Erycina
Helicina?
Murex nodularius
Melania? They are however too much injured about the mouth to determine their genus with certainty
Another species of Melania corresponding to those of Plumstead
Natica Canrena	Nerita
Ostrea, approaching to deltoidea
– – – – specific characters not evident, but different from the last.

Fossils found at Harwich in Essex

Names given by Lamarck.	Linnean names.
	Patella ungaria
	– – – – lævis
Patella spirorostris	– – – – fusca
Fissurella labiata	Patella
– – – – – emarginula	– – – – fissura
Calyptrea sinenis	– – – – sinensis
Eburna glabrata	Buccinum glabratum
⁠– – – –	Murex corneus
⁠– – – –	– – – – erinaceus
⁠– – – –	– – – – contrarius
⁠– – – –	Trochus sulcatus
⁠– – – –	– – – – – alligatus
Ampullaria rugosa
Natica canrena
– – – — glaucina
Mactra
Venericardia senilis	Arca senilis
Lucina	Venus gallina
– – –	Solen siliqua
Pholas crispata
– – –⁠– – –	Ostrea deformis
Pecten plebeius
– – – infirmatus
Balanus

Some of these however may belong to the lower marine blue clay.

M. Brongniart mentions the following as being found in the
⁠various beds of the upper marine marls.

Cytherea (bom-bees)	Ostrea Hippopus
– – – – – plana	– – – – Pseudochama
– – – – – elegans	– – – – longirostris
– – – – – semisulcata	– – – – canalis
Cerithium plicatum	– – – – cochlearia
– – – – – cinctum	– – – – cyathella
Ampullaria patula	– – – – spatulata
Cardium obliquum	– – – – linguatula
Nucula margaritacea	Bones and parts of Fishes
Patella spirorostris—Cuv. p. 187.
In the upper marine sand stones.
Oliva mitreola	Pectunculus pulvinatus
Fusus, resembling longævus	Crassatella compressa?
Cerithium cristatum	Donax retusa?
– – – – – – lamellosum	Cytherea nitidula
– – – – – – mutabile?	– – – – – lævigata
Solarium?	– – – – – elegans?
Melania costellata?	Corbula rugosa
Melania?	Ostrea flabellula

I have already mentioned that considerable difficulties appear to me to exist in assigning a place to the Woolwich beds. The actual lowness of their level, appearing to dip under the London clay, and their situation near the chalk without the intervention of that bed, at first seem to determine their geognostic position. Whilst the circumstances of their not being seen in any part covered by the London clay, nor having been actually identified with any strata which have been found in sinking through it with certainty, leave the question still undetermined; and the agreement of the fossils of the Woolwich and Plumstead beds with those of the upper marine formation in the Isle of Wight, not only in their species but in their state of preservation, is sufficiently striking to suggest the idea of a similarity in the circumstances of their production.

The considerably greater elevation of Highgate-hill, and of other places known to consist of the London clay, above the Woolwich beds, is scarcely of itself a satisfactory reason for supposing that the latter exist under the former, since the changes to which this part from the chalk upwards has been subjected at various periods, are sufficiently pointed out by the extensive banks of pebbles of very ancient date, and the other proofs of the agency of water. The great irregularity in the surface of the chalk stratum is obvious from its disappearing so suddenly on the north bank of the Thames; and it is not difficult to imagine that from currents and other local causes, the deposition of the London clay might not have taken place in certain spots, which might yet have been covered by the sea that gave rise to the upper marine stratum on the Isle of Wight. It must be confessed however, that for want of proper sections, we have not yet sufficient data for determining this point with accuracy, and I shall content myself at present with having described such facts as I have myself noticed, leaving this subject to future investigation.

Mr. Parkinson enumerates the following as found at Woolwich.

Names given by Lamarck.	Linnean names.
Cerithium turritellatum	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,}$ Murices
– – – – – denticulatum
– – – – – serratum
– – – – – claviculatum
– – – – – mutabile
– – – – – cinctum
– – – – – semicoronatum
Cytherea scutellaria	Venus
Cyclas deltoidea
Calyptrea trochiformis	Trochus apertus
⁠to which I have added
Ancilla Buccinoides	Voluta
At Plumstead.
Melania	Helix
Arca	Arca
Ampullaria	Helix
Calyptrea trochiformis
Cyclas
⁠and Mr. Parkinson has since found
Nucula margaritacea	Arca nucleus
Teeth of fishes
At Newhaven.
Cerithium denticulatum	Murex
Cytherea scutellaria	Venus
Ostrea	Ostrea

In the Paris basin the marine marls are covered by a very extensive and thick bed of sand, entirely without animal exuviæ, which has nearly filled up all the cavities which still existed on the surface of the basin, covering the partial formations of marine gypsums, the lower freshwater marls, together with all the other strata, and reducing the surface nearly to a level.

This sand frequently contains beds of sandstone of the same nature with itself, which frequently form the flanks of the hills in the neighbourhood of Paris; and great blocks of these have frequently rolled down into the valleys, the sand having been carried away; such are the sandstones in the forest of Fontainebleau, Palaiseau, &c. The sand of this stratum is often an extremely pure white quartz, and is much used in the arts; but sometimes it is coloured by oxides of iron, or impregnated by carbonat of lime. It forms all the soil of Beauce. The sandstone is very hard, pure, and homogeneous.

This bed is usually covered only by the burr stones without shells, or by the upper freshwater formation. Over it however there is in some parts a sandstone containing marine shells, agreeing nearly with those of the middle beds of the calcaire grossier, or rather with those already observed in this upper marine formation; and in other places a calcareous stratum with shells.

The London clay is in many places covered by an extensive bed of sand, usually called the Bagshot sand. It extends over Bagshot, Frimby, and Purbright heaths, in the county of Surrey, and that on Hampstead heath belongs also to it.

At Purbright, and many parts of the surrounding country, loose blocks of a stone is found similar to what has been called the grey weathers. This stone, composed of siliceous particles cemented together without any intervening substance, may be considered as a granular quartz. It has more the appearance of an original formation, or peculiar crystallization of siliceous matter analogous to that of sugar, than to a substance composed of the detritus of other rocks.

Numerous large and loose masses of this rock lie scattered over the surface of the chalk country, particularly in Berkshire and Wiltshire, but a bed or continuous stratum of it has not yet been observed. These stones were much employed by our ancestors in building, and before the ground was cleared for the purposes of agriculture they were much more numerous than at present. The huge erections of Stonehenge, which have so much exercised the conjectures of our antiquaries, are chiefly^[16] composed of it, and the blocks were no doubt found on the spot.

This granular quartz bears a close resemblance to the siliceous cement of the Hertfordshire pudding-stone, which also is often found in loose masses above the London clay. There appears no necessary connexion between the pebbles of this beautiful conglomerate and their cement, but the dates of their origins were very different; the siliceous deposition, when it did not envelope any foreign substance, forming the rock called the grey weather; and when it fell among pebbles of any kind, composing a pudding stone. Accordingly we sometimes find in the grey weathers common chalk flints.^[17]

§ 5. Upper Freshwater Formation.

I have now to describe the most remarkable and best characterized of all the strata in that hill in the Isle of Wight called Headen, which has so frequently come under our examination.

Here, immediately over the last-mentioned formation, there is a thin bed of sand of 6 inches, upon which rests immediately a very extensive calcareous stratum 55 feet in thickness, every part of which contains freshwater shells in great abundance, without any admixture whatever of marine exuviæ.

The substance of which this stratum consists is of various character, although it cannot be described as being subdivided into smaller beds. A great part is composed of a yellowish white marl, sufficiently indurated to remain in blocks when fallen down, but extremely friable, and which, like other marls, will not endure the frost. In this, and disposed without any regularity, are hard masses of a rock which appears to contain a greater proportion of calcareous matter; and to be in about an equal quantity with the marl. This stone is very durable, and is employed as a building material. Between these two extremes there are many parts of intermediate degrees of hardness and durability.

Many of the shells which are found imbedded in this stratum are quite entire, and these are mixed with numerous fragments of the same species. They consist, like the lower freshwater formation, of several kinds of lymnei, helices, and planorbes, and from the perfect state of preservation in which they are found, must evidently have lived in the very spots where they now are, the shells of these animals being so friable that they could not have admitted of removal from their original situations without being broken.

These organic remains therefore most distinctly mark the nature of the place where the strata enveloping them have been deposited. It must unquestionably have been the bosom of an extensive lake in some period of the earth far antecedent to human history; nor can we refrain from emotions of extreme astonishment when this conviction is forced upon us, nor help indulging in speculations on the revolutions which the earth must have undergone, when we consider how very differently these strata are now situated. Instead of being found in a hollow, they now compose the upper part of a hill; nor are they any more surrounded by those elevations which must have been essential to the confinement of the vast body of fresh water which furnished a habitation to myriads of animated beings, and of which we have nothing to demonstrate the former existence, except the nature of its depositions, which remain a faithful record.

Over this bed is a stratum of clay 11 feet in thickness, containing numerous fragments of a small bivalve shell. The hinge of this shell is of so peculiar a structure that Mr. Parkinson was not able to refer it to any known genus. The shells are thin, and unmixed with any other species whatever. It is impossible therefore to say whether they have belonged to marine or freshwater animals, and I have preferred for the present to keep them among the latter, rather than to suppose another alternation of which there is no direct proof.

Upon this lies another bed of yellow clay without shells, and then a stratum of friable calcareous sandstone, also without shells.

To this sandstone succeed other calcareous strata having a few freshwater shells. In these, which, like those mentioned above, are not subdivided into distinct beds, are parts of extreme compactness, so as to acquire a porcellanous character. Other parts contain masses of loose chalky matter, most of which are of a roundish form; and among these also are many beds of a calcareous matter, extremely dense, and much resembling those incrustations that have been formed by deposition from water on the walls of ancient buildings in Italy.

Through all these last strata are veins, frequently several inches in thickness, of very pure carbonate of lime, which is crystallized, frequently in a radiated form.

This stratum may be seen in many parts of the Isle of Wight, north of the middle range of chalk hills. On the western coast it does not extend farther than Totland bay, but occurs again at Warden point, forming the summit of the cliff.

Numerous blocks of it lie loose in the soil in many parts about Cowes, Binstead, and Bembridge. But in the neighbourhood of Calbourne, and between that place and Thorley, several quarries are opened in it, and afford an excellent stone. The fossil shells are here larger than I have observed them in any other part, the planorbes being full two inches in diameter, and the cyclostomæ nearly as large. The rocks at Bembridge ledge and Whitecliff bay, on the east side of the island, must also be referred to this formation.

It appears therefore to have originally extended over the whole of the northern half of the island; but I have not yet been able to find it on this side of the water, and it is still uncertain whether it ever existed here, or whether it has disappeared amidst the last revolutions to which the surface of the earth has been subjected.

This formation may be considered as the latest in this country which we have as yet been able to detect: and of all those above described it agrees most nearly with its corresponding formation in the Paris basin, with this difference however, that none of ours is siliceous; I shall therefore, in the succeeding comparison, confine myself to the calcareous part.

The external characters of this in both countries are sufficiently different from every other known rock to render them distinguishable even without the shells. That of France is described as white, or yellowish; sometimes as tender and friable as chalk or marl, and sometimes very hard, compact and solid, with a fine grain and conchoidal fracture. In the latter case it breaks into sharp fragments like flint, and cannot be worked as stone; sometimes it will even admit of being polished as marble. It is also frequently filled with infiltrations of calcareous spar.

This description corresponds very nearly with the freshwater of the Isle of Wight, and an examination of the specimens from both places leaves no room to doubt of the similarity of the strata.

The fossil shells which I found in the upper freshwater formation, and which have been described by Mr. Parkinson, are the following.

Names given by Lamarck.	Linnean names.
Planorbis, much resembling that which Brongniart says approaches to P. cornu	$\left.{\begin{matrix}\ \\\ \\\ \end{matrix}}\right\}$	Helix planorbis
Planorbis, two other species
Planorbis, much resembling P. prevostinus
Ampullaria	Helix
Cyclostoma	Helix
Limneus longiscatus	Helix
────── acuminatus

Limneus	corneus
	perhaps a large specimen of L. longiscatus
Gyrogonites

Striated seeds of a flattened oval form, with parts of coleopterous insects. ^[18]

M. Brongniart has enumerated the following fossils as belonging to this formation.

Cyclostoma elegans antiquum	Limneus inflatus
Potamides Lamarckii[19]	Bulimus pygmeus
Planorbis rotundatus	– – – – – terebra
– – – – – cornu	Pupa Defrancii
– – – – – prevostinus	Helix lemani
Limneus corneus	– – – Desmarestina
– – – – – fabulum	Gyrogonites
– – – – – ventricosus

The last mentioned fossil, to which Lamarck has given the name of Gyrogonites, is a small globular canellated body about the size of a mustard seed. The specimens of the French fossils of this species, in the possession of the Society, are extremely perfect, and correspond exactly to those which I found. They are very numerous in the freshwater stone at Gurnet point; but they are there only to be seen as casts. In the numerous portions of a thin calcareous bed of a highly crystalline structure which lie scattered on the shore at Cowes, (but which I have not been able to find in situ) these Gyrogonites are found mixed with cerithia, bivalves, and a species of serpula; all these shells being in a whitened state. This fossil was formerly placed by the French naturalists among the multilocular shells, but from a late number of the Journal de Physique, it appears that recent observations have shown it to be the petrified seed of a species of chara.

It is singular that the Calcaire d'eau douce of the basins of Paris and of the Isle of Wight, though found so abundantly in both countries and constantly used as a building material, should have so long escaped the observation of naturalists. At the latter place it has been employed for building from time immemorial, not only in that island but in many places on this side of the channel, as at Portsmouth, Southampton, Lymington, &c.

§ 6. Alluvium.

Under this title may be comprehended all those collections of various materials, which have been transported at some former period from different parts of the globe, and deposited on the surface.

The whole of it is evidently composed of the detritus or fragments of substances which have been originally formed into regular strata, but which have been torn up and confusedly mixed together by violent and extraordinary causes, or gradually accumulated by rivers or meteoric agents. It is therefore, as might be expected, extremely various, according to the nature of the strata from which it has been derived.

Considered in this point of view the study of it becomes particularly interesting, since it enables us to trace back, in some degree, the great changes which have taken place upon the surface of the earth.

In that part of our island which we are now considering, this alluvium or covering is of a nature peculiar to it. Besides the vegetable earth, clays, marls, and sands, which it possesses in common with other places, it is distinguished by a vast quantity of rounded siliceous pebbles of various kinds and sizes, which lie distributed in a very unequal manner, sometimes forming thick beds intermingled with clay, sand, and small sharp fragments of flints, at other places mixed with shells of various kinds, and sometimes almost without any other substance. This compound is termed Flint gravel.

When we observe a heap of these pebbles, we easily see that they consist of a great variety of kinds, and upon attentively examining them we are able to reduce this variety to several classes.

Some are evidently fragments of the flinty nodules originally belonging to the chalk strata. This is evinced by their mineralogical characters, their sharp conchoidal fracture, peculiar black colour, and by portions of the white crusts with which they were invested while in the chalk beds still remaining attached to them.

In others this origin is not so evident, the crusts having been entirely worn off, and the fragments themselves rounded by attrition. Yet their fracture, colour, and other circumstances, oblige us to suppose that these also were derived from the chalk. In many places the whole or the greater part of the gravel consists of these rounded chalk flints; and hence probably some have been induced to suppose that all the pebbles of the London gravel have proceeded from the same source.

But besides these other siliceous nodules occur, the origin of which is not so evident, as they differ in many respects from the chalk flints in their usual state. Of these some are of a deep red colour with a great degree of transparency resembling carnelian: others are of a yellow chalcedony often translucent and even botryoidal, and they pass into a kind that is yellow, opake, and of a waxy lustre. Others again appear to be nearly allied to hornstone, and are frequently of irregular shapes, which are probably those of the original nodules.

Another remarkable class of siliceous pebbles is found either mixed with all those above mentioned, or alone, or cemented together into a pending-stone. These appear to have been originally formed of concentric coats or layers of different colours, which vary in almost every specimen. The colours are for the most part yellow, brown, red, bluish-black, grey, and white: but these run into each other by an infinite number of shades. Others are spotted or clouded with different tints, and have much the appearance of Egyptian pebbles. They take an excellent polish, and are then often extremely beautiful.

These last appear rather more to resemble agates than chalk flints. They are never found of a large size, seldom exceeding two inches in diameter, and generally are not more than one inch: they are of an oval or flattened form, which appears to have been their original figure, although they have evidently been subjected to a certain degree of attrition.

All the above mentioned pebbles are sometimes surrounded by crusts; and it does not appear clear whether these are not sometimes original, though perhaps stained by the ochreous substances in which they have been imbedded, or whether they are generally the effect of decomposition. Flint appears to be one of the most unchangeable substances with which we are acquainted. We see buildings constructed with flints that have resisted the agency of the atmosphere for many centuries without undergoing the smallest visible alteration, or having become whitened in the least degree. It is however well known to be liable to decomposition under certain circumstances; and it must be allowed that the combined action of moisture and various decomposing causes whilst a mineral remains buried in the soil, may produce effects which we can scarcely estimate.

Upon the whole, however, it appears to be extremely improbable, that any species of imaginable action could have converted a fragment of chalk flint into a substance so very different as one of the rounded concentric pebbles of the London gravel.

To assist us in endeavouring to obtain a just idea with respect to the origin of the different accumulations which are found in our gravel, it may be useful to consider the various changes which have taken place in our upper strata. Of these, although ignorant of their causes or their extent, we yet perceive the traces written in characters sufficiently legible.

Although the chalk has been originally formed at the bottom of the ocean, yet from some change which took place either in the level of the sea, or in the state of the strata, part of it probably at an early period has been above, and part below, the surface of the water, as at present; and this before the deposition of those strata which we now see immediately superimposed upon it.

From that date, and by the same cause as we see still producing this effect, did probably the formation of rounded flint pebbles begin. The chalk itself, being easily acted upon by the waves, became disintegrated, while the siliceous nodules were better able to resist this abrasion, though yet liable to be broken and rounded by friction against each other.

This effect takes place chiefly upon the margin of the sea. In deep water it may in some degree be produced by the action of the tides; but it is by the irresistible force of the billows and breakers that it proceeds with the utmost rapidity. Hence all geologists, in examining the history of the strata, have considered rounded pebbles as proofs of the existence of land elevated above the water.

At this remote period of the earth, when the outline of the coasts were, as now, deeply indented by gulphs and bays, but whose forms and situations had but little if any correspondence with the present, great changes must have taken place by the gradual action of the sea; and vast accumulations of pebbles of different materials, formed by attrition, would be thrown upon the shores.

In the ancient Parisian gulph this phenomenon is distinctly pointed out; nor are similar appearances wanting to demonstrate the action of the same causes in the Isle of Wight and London basins.

We have seen that in Alum bay there are layers of rounded pebbles in the vertical sand strata, which must have been formed prior to the subversion of the chalk, and before the deposition of the London clay. Similar rounded flints, and often of a whitened appearance, are found in the sand strata at the bottom of the blue clay in various parts of the London basin.

All these belong to the most ancient flint pebbles, formed by the same sea that deposited our blue clay and the calcaire grossier of France.

The thick bank of flint pebbles at Woolwich and Blackheath, separated from the chalk only by sand, appears like the section of an ancient beach, it being not far distant from the shores of the ancient marine gulph or bay which now forms the London basin. The fossil shells which we see in such numbers among these pebbles are almost all partly broken, and lie exactly in that confusion in which they appear when thrown up by the sea upon the shore. Water-worn pebbles are mentioned as occurring in the lower beds of the French calcaire grossier, and a number of other examples might be adduced; but these are sufficient to shew the contemporaneous agency of similar causes in different places. Prodigious banks of such pebbles are thrown up on our shores at the present time, and may serve very well to explain the origin of these ancient formations of flint gravel.

But with respect to the concentric pebbles above described, conceiving it to be improbable that they have been derived from chalk flints, I am compelled to look for their origin to some other source.

Considering them, as well as all the other bodies composing the alluvium, as detritus or ruin, a circumstance sufficiently shewn by the confused manner in which they lie, and by the water-worn appearance of a great part of them, it is unnecessary for us to confine ourselves to the chalk in seeking for the beds to which they originally belonged.

Siliceous nodules are frequent in other limestone strata; an excellent instance of which may be seen at Tillywhim quarry in the Isle of Purbeck. Trap also, as is well known, forms the matrix from which many agates are derived. Various silices, such as the carnelian, onyx and agate, invested with the usual crusts, are described by De Luc as being spread over the hills near a part of the course of the Rhine, while there are not in Europe any known natural strata that contain these stones.

One of the most remarkable circumstances in which the basin of the Isle of Wight differs from that of Paris, is the absence in the former of those siliceous formations so abundant in the latter. The siliceous limestone, which contains also a burr-stone, covers half the bottom of the Paris basin. In the middle and upper beds of the calcaire grossier they have hornstone, and the nectic and lenticular quartz. The singular substance, called silex menilites, is well known to all mineralogists: it is found in the foliated argillaceous marls of the gypsums. In these marls they have also siliceous nodules, which are white, opake, flat, and mammillated, and also beds of flint. Silicified trunks of trees are also described. The meuliere without shells, above the upper marine formation, passes often into the state of flint, sometimes white and opake, and sometimes grey and translucent.

In their upper freshwater formation, a siliceous part containing the same shells as the calcareous is very abundant. The description of the several varieties of flints in these beds is as follows.

1. Flint, of a grey colour, translucent, fracture close and waxy, and even horny.
2. Flint, yellow, very translucent, very easy to break, fracture conchoidal and smooth.
3. A jasper flint of an opake whiteness like wax, fracture waxy and scaly, possessing little frangibility.
4. An opake jasper flint, a little cellular, and having all the characters of a compact burr-stone.

Such is the imperfection of language, that a correspondence merely in the general description of two mineral substances, is not sufficient to enable us to ascertain their identity. It must be allowed however, that most of the characters above enumerated will apply very accurately to many of the flints which I have described as composing the greatest part of some heaps of our gravel. I have also found among these many water-worn fragments of a siliceous stone that bears a considerable resemblance to the French meuliere or burr-stone.

If therefore we admit that the pebbles of our gravel are derived from the destruction of former strata, that many of them differ from any other siliceous bodies with which we are acquainted, and that these bear perhaps a stronger resemblance to the flints of the Paris beds than to those of the chalk (judging from some specimens of French flints in the Museum of the Geological Society), and if we have reason to believe that some of those beds formerly existed in this country, will it be considered as a conjecture rash and unwarranted, should I imagine that the substances in question have derived their origin from siliceous nodules, originally formed in strata which existed over our blue clay, but which have been disintegrated, and carried off, in one of those revolutions to which this part of the earth has been subjected?^[20]

The formation of the nodules of flint in chalk has frequently, and will probably much longer continue to excite the speculations of philosophers. But whatever was the mode in which they originated, we may fairly imagine that these siliceous masses in question now found in our gravel, (but which I have supposed to have belonged originally to regular strata) were formed in a similar manner.

The coats of the flints in chalk have been found by chemical analysis to consist of chalk mixed with the flint; and it appears that all nodules formed in a matrix have crusts or coats, composed of a combination between the matter of the nodule and the enveloping substance.

The coats of these pebbles may be supposed therefore to exhibit a similar phenomenon; and in them we may perhaps see a part of the stratum which they were at first imbedded in.

If it be asked what has become of the supposed matrix in which these flints were formed, and how could strata so considerable as they must have been, have disappeared without leaving a single trace of their existence? It may be answered, that the difficulty is exactly the same in supposing them to be derived from the chalk; for no remains of this rock are to be found with these pebbles; and it is equally impossible to discover what has become of the chalk that must have belonged to the flint pebbles that are undoubtedly derived from it.

But when we see rolled pieces of granite, of quartz, and other primitive rocks, occurring frequently in the alluvium of this part of the country, though so far removed from the places where these substances are in situ, we feel so assured of the extensive nature and violent action of the cause that has occasioned such destruction, that we need not wonder if many strata have been reduced to a state of impalpable division, and have been scattered over the surface, so that not a fragment remains entire; or have been deposited in the depths of the ocean, where they may have formed new combinations that may at some distant period be exposed to view, and afford matter for the contemplation of future generations. The Hertfordshire pudding-stone has been already mentioned. It is composed of these concentric pebbles united by a granular quartz, and is most abundant in the neighbourhood of St. Alban's, but is found in many other places above the chalk. It occurs in large irregular masses in the gravel; but I am not aware that it exists any where in an extensive bed in situ.

To account for the appearance of this pudding-stone we have to suppose, 1st, the existence of a stratum superior to the chalk, containing under some form, the substance of which these pebbles are composed. 2d, the agency of some power capable of breaking up this stratum, of reducing it to fragments, and of disintegrating it, by removing the matrix containing the siliceous matter. And 3d. the deposition, either partial or general, of a solution of siliceous earth capable of cementing the whole together into one mass.

This formation is no doubt of ancient date, and long anterior to that of the present surface of the earth; a circumstance which is rendered probable by our finding masses of this pudding-stone itself water-worn, indicating, that since its cementation it has been subjected to some of these revolutionary processes, of which we have seen so many other proofs.

That all the ancient pebbles were not cemented together in a similar manner, is shewn by those in Alum bay, which are in loose sand; and by those which are found in the beds of sand in the blue clay, both in the neighbourhood of London and at Portsmouth.

But that some of the gravel may have been at a former period in the state of pudding-stone, and may have been disintegrated, is a circumstance also highly probable. Yet there does not appear any necessity for supposing that all our gravel has been originally pudding-stone, any more than that all sand has been sand-stone.

Another species of pebble which is very common, is a striped flint, or rather a kind of hornstone. These appear never to have had crusts, but owe their rounded forms entirely to the action of water. They may be supposed to have been derived from a bed of such a substance, which has been reduced to fragments. Beds of a striped chert very analogous to this I have seen in the island of Portland, alternating with the oolite.

Turf, so abundant in the north of France, is much less frequently seen in this part of England. The practice of draining, and the great attention paid to agriculture in our country, have much diminished the quantity of morasses and ancient depositions of this kind; and the great superiority of coal as a fuel, and which gives us a natural advantage over other nations, has rendered turf of little value.

In Lincolnshire however the quantity of marsh land is prodigious; and the well known and accurately described submarine forest, yet to be seen in that county, has already excited the attention of some of our naturalists.

The subject of the Fossil organic remains, found in the gravel, has been already so ably treated by a naturalist eminently qualified to do it justice, that I should have left the subject in better hands, did it not form so essential a part of an account of our upper strata, that to have omitted it entirely would have rendered some of the following observations less intelligible.

From the view which I have taken of the subject, it will be seen that I consider the fossil shells found in the gravel, as well as the gravel itself, as exhibiting proofs of the detritus or ruin of ancient errata. Hence specimens of all those fossils which belonged to the strata over the chalk may be expected to be found in it.

I am aware that the perfect state in which many of these fossil shells yet remain, has been considered as a proof that they have never suffered a removal, but that they have lived and died upon the spots where they now are.

That this is the case with some of the upper beds containing fossil shells, as the thin clay strata of Woolwich, Plumstead, &c. and perhaps of other places with which I am not acquainted, there can be no doubt. But the same argument will not apply to such as are surrounded by, and enveloped in, beds of water-worn pebbles and sand, which is evidently a confused mass, the consequence of ancient and violent changes, or the action of causes similar to what we perceive at the present day.

And if we reflect upon the manner in which the most delicate recent shells are buried when thrown upon the shore, in the sand and shingles of a beach, without being much mutilated, we shall not find it difficult to comprehend how very perfect specimens may sometimes be met with even in our gravel.

By attending to the revolutions that have happened to these upper strata, this subject will perhaps be less difficult to understand. Beds of gravel and sand containing fossil shells will be esteemed as the monuments of ancient changes though of different periods. But those shells grouped in families and contained in beds of foliated clay and marl, may be considered as still remaining in their original situations.

By this distinction we shall be able to separate real alluvial fossils, or such as have been washed out of regular strata from those that have never been disturbed; and the various states of violent convulsion, as well as of quiescence, which the ocean must have experienced during the several eras, the geological history of which we have been considering, are sufficient to account for these appearances.

In a work lately published by an eminent fossilist, I have met with an opinion, that all the spoils of terrestrial and submarine productions which we find buried in the strata in this country over the chalk, have been transported from distant climates, and have been deposited in a tumultuous manner by some great convulsion that blended them in one common grave. I should not have thought it necessary to allude to this idea, if I had not understood that it has been considered by some as demonstrating that all the strata over our chalk are alluvial.

The grounds upon which this supposition is made, is the observation that the recent analogues of most of these fossils are now inhabitants of the torrid zone. The extreme delicacy however of most of these shells, as well as their perfect preservation (as Mr. Parkinson has already observed,) precludes entirely the possibility of their having been brought from distant places, and they serve merely to shew that this part of the globe must be very different, relatively to such species of animals, from what it was at the period of their entombment.

In some beds of pebbles and gravel fossil shells are very numerous, as in those of Woolwich, Harwich, &c. and with these alternate frequently beds of clay and sand, containing shells regularly distributed, entire, and apparently undisturbed. Of these shells Mr. Parkinson observes, some belong to species now only found in distant seas, and others appear “not to differ specifically, as far as their altered state will allow of determining, from the recent shells of the neighbouring sea.”

But granting, as we must, that the formation of pebbles has taken place at different periods, it must be extremely difficult, and perhaps impossible in all cases, to distinguish whether they are now to be seen in the places where they were at first deposited, or whether they may not have repeatedly been moved.

In many beds of gravel delicate shells are so abundant that the cause which placed them there could not have been very violent; whilst others are found totally destitute of organic remains, except such as are impressed upon the substance of the pebbles themselves. Among the latter may be enumerated, pectines, anomiæ, the interior casts of echini, and impressions of the spines and plates; zoophytes of unknown genera, some resembling alcyonia, are also frequent. It does not appear certain whether all these may not have belonged to the chalk strata, but Mr. Parkinson is of opinion that some differences are observable between these echini and those of the chalk. M. Desmarets has described in the lower gypsums of Montmartre fossils similar to those of Grignion, many of which are echini of the genus spatangus, but different from the spatangus cor anguinum found in the chalk. At Grignion too, there are echini which belong no the genus clypeastra.

Impressions of organic remains very rarely occur in the concentric pebbles, particularly those of the Hertfordshire pudding-stone;^[21] but the yellow calcedonic flints frequently contain alcyonia.

The Fossil-bones of quadrupeds are frequently found in the alluvium of this part of England, and they appear to be of several dates.

The most ancient are entirely petrified, and where found in the gravel, appear to have been washed out of the strata in which they were originally imbedded, which, from the part of the matrix still adhering to them, appears to have been calcareous. Mr. Parkinson has described some of those found at Walton and Harwich, which however were too much broken to enable him to ascertain distinctly the animal to which they belonged, but he conjectures them to be parts of the Mastodon of Cuvier.

The next class contains the bones of the elephant, rhinoceros, hippopotamus, and the Irish elk, which are no longer natives of this climate. These however are not petrified, and though generally in a state of decay yet are sometimes quite perfect. They are particularly abundant in Suffolk and Norfolk; but have also been found at Brentford, in the Isle of Sheppey, and several other places. And it is particularly important to remark that these are never found in the stratum of London clay, but always upon it, and frequently accompanied by marl and freshwater shells.

Other bones of ruminating animals, as those of the horse, ox, and stag, not different from the living species, are frequently dug up at small depths, and are covered by peat, gravel, loam, &c.

In the freshwater formations of the basin of Paris the bones of terrestrial animals are found, which do not belong even to known genera, and many of those found near the surface in their alluvium, belonged also to animals of great size, and which are now found only in countries very remote.

We see therefore that a similar succession of animals has lived in this portion of the earth, during the various stages of its habitable state.

V. Concluding Observations.

One of the most interesting consequences deducible from the above examination of the last formed strata of this country, is, perhaps, the view which it seems to afford us, of establishing, in some degree, a series of epochs between the deposition of the chalk strata and the formation of the present surface of the land; not indeed to be distinguished by computable time, since no date can be affixed to any of the changes to which I have alluded, but an order of succession of the great events at least appears more than hypothetical, which it may be useful still further to consider.

The origin of the calcareous matter of which the chalk formation is composed remains one of those hidden mysteries on which all the speculations of geologists have not thrown any certain light.

In the several strata of chalk however, although their sources were probably not very different, we may perceive several circumstances which indicate the action of modifying causes in each deposition, that seem to have had considerable influence upon organic life. The almost entire absence in the lower beds of those siliceous nodules that are so numerous in the upper one, and the remarkable differences in their animal remains, furnish sufficient reasons for this supposition.

Calcareous, argillaceous and siliceous matter, the whole or a part of which was in a state of solution, originally formed the mass of this formation. Of these the argillaceous seems to have subsided first, but more or less mixed with calcareous earth. The silex now occupies the upper division, but whether separated by the action of chemical affinities, or introduced subsequently, does not yet appear. The tranquil state of the ocean during this period may be inferred from the perfect preservation of the numerous delicate fossil organic bodies now found in the chalk.

An era of turbulence seems to have succeeded; during which however the depositions of the plastic clay and sand denote certain intervals of repose. The surface of the chalk already solidified was in a certain degree, though irregularly, subjected to the agency of water in motion; and other causes might have combined in destroying the original horizontality of its position. But where the vast bed of London clay subsided, the sea must have regained its former tranquility.

The numerous vestiges of vegetables as well as of animals to be found in this stratum, whose recent analogues are now seen only in tropical countries, involuntarily leads the mind to contemplate with wonder the altered condition of this portion of the globe. Have the laws which regulate the place and motions of this earth in the system of the universe been subjected to change? Are there in these any sources of irregularity or gradual alteration, the proofs of which can be detected? these are questions for astronomers.

If we consider that the flinty chalk is somewhat above the level of the sea at Woolwich and Gravesend; that it dips under the Isle of Sheppey and disappears; that at Margate it has been so elevated that a considerable part of the lower chalk is now seen, the whole of the upper or flinty chalk being gone; that at Dover it rises to a vast height; that on the north side of the Thames it appears at Purfleet opposite to Gravesend, but immediately disappears to rise no more on the coasts of Essex and Suffolk.—If we reflect on the rapid dip of the chalk at the Hog's back, between Guildford and Farnham, with the many hills and hummocks of chalk to be seen in the counties of Suffolk, Norfolk, &c. we may perceive evident proofs of the great irregularity of the ancient surface of this stratum, and a part of the elements which may enable us to trace the limits of the land and sea at that period.

In speaking of the formation of the gravel, the probable mode has been detailed, by which the mountains of chalk originally appearing above the sea may have been worn away, cliffs have been formed, and the flints broken and rounded into pebbles. Of the early existence of this process, we have seen proofs in the vertical bed of pebbles of Alum bay, and in those frequently found in the sand of the plastic and blue clay in many other places. And also in the lower beds of the calcaire grossier of the basin of Paris.

We have seen also that the extraordinary event of the elevation or subsidence of the chalk of the Isle of Wight and Dorsetshire must have taken place after the deposition of the great stratum of blue clay.

A change of this kind, of which we have no parallel in human record, it would be in vain to endeavour to account for; but it must have been an event of itself sufficient to produce great changes in this part of the globe, and must have been accompanied by the most extraordinary phenomena. From the correspondence in the situation of the chalk and the accompanying strata in the Isle of Wight and Dorsetshire, it should seem, that the range of chalk hills in each of these places was at first united; and thus a marine gulph was formed, open to the east, in which a part of the depositions at that time going on in the ocean subsided.

The observations of several geologists have shewn the natural tendency which the sea has to fill up æstuaries, and to throw up bars across their mouths by the accumulation of pebbles and sand. Many remarkable instances of this process have been observed on the shores of the Baltic, and even in this country. It appears also that such gulphs and bays are frequently converted into freshwater lakes, of which Loo Poole in Cornwall is an excellent example.

As it is most philosophical to seek for the solution of natural phenomena from known causes, might we not suppose that a similar circumstance has converted the gulph we have contemplated (now partly occupied by the Solent) into a lake of fresh water? If the size of the bar necessary for this purpose should appear extraordinary, we have only to recollect the Chesil bank, which now joins the Isle of Portland to the main land; and many others of the same description.

With this subject in my mind, while examining the cliff at Brighton, which has been already described, I could not resist the idea that it might possibly be the remains of this ancient inclosure of the lake. That it exhibits the vestiges of a vast and ancient accumulation well fitted for this purpose, there can be little doubt; and it is evident, that it has extended in the necessary direction, it being now a vertical section of what must have run out far into the sea.

Whether such a supposition as this can afford a solution of the phenomenon of strata formed in freshwater appearing over marine strata, I shall leave to be determined by those who are competent to such a task.

Of the unfathomable antiquity of these great and numerous collections of freshwater in the ancient world we have however abundant proofs, in the admirable researches of Cuvier on the extinct genera of animals which inhabited their borders.

It would perhaps be impossible for us now clearly to ascertain what could have furnished the prodigious quantity of calcareous, and still more the siliceous matter which they held completely in solution; in modern lakes we have examples of strata now forming of marle arising from the shells of the numerous freshwater animals which inhabit these shells, but these beds (as far as is yet known) are not consolidated.

Was a portion of the calcareous part of these ancient strata derived from the surrounding calcareous hills, which might have been lofty? If we examine the section of the Isle of Wight, the probability appears considerable, that the strata of chalk must have stood at a considerable height above the lake; although it has subsequently undergone the same levelling process, to which all the surface of the island has been subjected.

As connected with this subject, I shall quote a passage from Bergman's Physical Geography published in Swedish in 1769.

“At Langesaltza in Thuringia, they find under the vegetable earth a calcareous and porous tufa; in other parts a fine white sand mixed with river shells; below, a bed of hard stone, under which is a bank of porous stone or sand. Lower still they find a bed of hard stone, then tender stone and sand; afterwards peat formed of a mixture of leaves, barks of wood, roots, river shells, &c. Lower, yellow sand; and finally, grey fullers' earth mixed with marine bodies. The thickness of the beds of stone varies from 6 to 12 feet. They contain river shells, bones, sculls of animals, kernels of fruits, ears of corn, &c. These strata extend quite under the city so the borders of the Unstrutt, near to which are seen strata of alabaster and limestone, the detritus of which has probably given origin to these beds. It is to be remarked that no remains of marine animals are found above the clay where the ancient beds commence.”

A very interesting account has been given by Von Buch of a freshwater formation in Locle in the district of Jura. It is contained in a high inclosed valley surrounded by mountains of white compact limestone; and consists of various alternating beds of marly limestone whitish and somewhat friable, bituminous shale, coal, hornstone of a smoke grey colour, and of a fine splintery or imperfectly conchoidal fracture, and containing crystals of quartz; also of opal of a brownish black colour, glistening lustre, and perfect conchoidal fracture. Both the limestone and hornstone contain freshwater shells, among which may be distinguished the helix cornea and bivalves.

From these and other accounts it appears probable that these freshwater formations were purely local, and there appears no necessity for supposing that the others were any thing more than local deposits in a former state of the earth.

I am aware that such formations have lately been traced on the shores of the Baltic, in the south of France, Spain, Germany, and Silesia; but this can only prove that fresh water lakes were in former times as at present very numerous and often extensive.

One of the most striking differences between these ancient lakes and modern ones, as has been remarked by Messrs. Cuvier and Brongniart, is the property possessed by the former of forming siliceous strata.

It would seem to have been a circumstance accompanying the last great revolution which the earth has undergone, that siliceous earth has been held less abundantly in solution since that period. That event appears to have been accompanied by a process of destruction merely; but former changes were alternately destructive and renovating or conservative. The animal and vegetable remains of the ancient world are frequently impregnated with siliceous matter. But I believe no well authenticated instances can be adduced of such a process going on in our times. Petrifaction, indeed, in the proper sense of the word, seems now to have entirely ceased.

In the strata over the chalk in France silicified organic bodies are abundant: in our upper strata they are rare, if we except those found in the gravel whose original situation is yet questionable. Indeed the only instance with which I am acquainted in this country in the strata over the chalk, are the siliceous fossils of Feversham already mentioned: some of these are entirely calcedonic.

The existence of the marine strata placed above the lower freshwater formation in this country, as well as in France, is a circumstance much more difficult to explain, and would seem to require either a rising of the sea or a sinking of the land in this part of the globe.

Alterations in the shape of the coasts, and the accumulation of sand and pebbles in various parts of the sea, affect the tides so considerably, as to occasion them to rise to very different heights at the same places at different periods; yet no change of this kind can be imagined sufficiently great to account for an effect so considerable as has been produced.

Instances of marine strata placed over those formed in fresh water have been observed not only here and in the basin of Paris, but in other places. One is mentioned by Professor Herman, of Strasburgh. The strata are situated in the department of the lower Rhine, in the mountains of St. Sebastian, one of the lowest in the chain of the Vosges.

The great quantities of white calcareous marl with freshwater shells, so frequently found on the top of the London clay, and enveloping the bones of land animals, would seem to denote a marshy country, and one containing a great deal of stagnant water. This seems to have been the first state of the country at the time of the emerging of the land after the deposition of the blue clay.

In this marl and over the clay is the first appearance of land quadrupeds, agreeing in this respect with the same observation made by Cuvier on the calcaire grossier, above which in France their remains are found in abundance.

The changes preceding or accompanying the upper marine formation perhaps destroyed part of the superior strata, and deposited many of those extensive beds of shells now to be found over the London clay. But the nature of the last original marine strata of this country, the revolutions they may have undergone even in the ancient state of the earth, are circumstances which can probably no longer be explained.

Whether the existence of the second freshwater formation in the Isle of Wight will admit of the same solution as has been proposed for the first, must be left, like it, undecided: but it appears to have taken place in a lake possessing the utmost tranquillity.

Upon the whole it must be allowed that the points of resemblance which have been enumerated between the superior strata of this part of our island and the adjoining part of the continent, are too numerous and striking to be the result of accidental causes, and demonstrate in the clearest manner that they were occasionally subjected to the same general laws. Whilst at the same time the variations are so considerable, that the effects of these causes appear to have been much modified by local circumstances.

But I shall now venture with less hesitation to draw an important conclusion from the section of the Isle of Wight, which has been already described, and which of itself forms a volume in which we may read the geological history of several of the latest revolutions which our earth has experienced.

The idea I allude to is, that the last freshwater formation, as well as all the other strata which we have been considering, is anterior to the great event which gave the last shape and surface to our land.

In the highly inclined and vertical positions of the strata of Alum bay, we see the effects of some great convulsion of nature, previous to the formation of the last strata.

In the horizontal deposits of the North side, we see strata of great extent and antiquity yet formed at a later period. But in the outline exhibited by the surface of the island, and which has no reference whatever to that of the strata, is plainly to be perceived the effect of a general and powerful agent, which has subsequently formed the whole of the contour by one bold and sweeping outline.

It may be interesting to see how the same result can be obtained by a careful survey of different portions of the globe.

Messrs. Cuvier and Brongniart have laid considerable stress on the observation, that the outline of the present surface has no resemblance whatever to the undulations of the strata derived from the irregularity of the bottom of the basin. But how much more striking is this in the Isle of Wight? By no ingenuity of reasoning can the present form of its surface be derived from the bottom of that ocean which deposited the chalk; nor would it be produced by any of the causes now acting; and nothing remains for us but to admit that it has been the effect of an extraordinary and an extensively acting cause.

In the smooth and undulating surface of the chalk hills, in the banks of gravel of great extent, in the deep hollows often filled up again by the detritus of regular strata, in the direction of the principal ridges and valleys, we cannot but recognize the effect of water, the only agent which we know to be capable of producing such appearances.

But under what influence has this power, fully equal to such a purpose, been directed? What could give sufficient energy to a body at other times so tranquil? These are questions of which the complete solution will perhaps ever remain in obscurity.

Yet already we have had sufficient proofs that the sea has not always maintained the same relative level; that it has alternately risen and fallen; although to ascertain the distance of time between these changes be absolutely beyond the reach of human sagacity.

Let us then imagine an ocean in a violent state of agitation. The hills of chalk, and the last depositions of the globe are torn to pieces; the flints are dispersed and rounded by attrition against each other; finally, currents carry them to great distances, and lodge them in hollows worn by the waters, or form them into ridges and other accumulations. Fragments of other rocks are intermixed; forests are torn up and levelled, and, with the vegetable soil, formed into morasses. The inhabitants of the land are destroyed and buried deep in this dreadful ruin. But a more surprizing revolution ensues. Disorder ends; the waters retire; the northern continents are disclosed, become fitted for vegetation, and are peopled by the tribes of animals which now inhabit them.

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1. A detailed description of the Isle of Wight is now preparing for the press by Sir Henry Englefield, who has permitted me to communicate to the Society many of the observations which I made at his request with the view of completing his work.
2. It was this chalk, together with the vertical strata of Alum bay, and the horizontal strata on each side, that were first observed and described by Sir H. Englefield.
3. Other divisions of these strata have been made, and the cause of the differences has already been alluded to. Not every member of the series is perfectly continuous or of uniform thickness; so that when any one is wanting, beds, usually separate, are brought into immediate contact. In making a classification of these beds, those should be considered as principal members, which are most rarely deficient in an extensive tract of country.
4. Having by the kindness of Mr. Holloway, of Portsmouth, become familiar with the fossils of Stubbington, I readily perceived their agreement with the above-mentioned stratum in Alum bay.
5. The drawings and description of this, as well as of many other parts of this remarkable coast, will be found in the above-mentioned work now preparing for publication, by Sir H. Englefield.
6. For the pointing out of this fact, as well as for much important information respecting the extent of the chalk, I am indebted to G. B. Greenough, Esq. V.P.G.S.
7. In using the word formation I have followed the example of M. M. Cuvier and Brongniart, who have employed it to express an assemblage of beds of the same nature, or of a different nature but formed during the same epoch.
8. A singular circumstance is mentioned respecting the chalk of France to which we have nothing analogous in this country. In Champagne there are immense plains of chalk absolutely deprived of vegetation, except where patches of the calcaire grossier occur as islands or oases in the midst of these deserts. And M. Cuvier observes that many parts of this tract have not perhaps been visited for ages by any living being: no motive existing that could induce any to wander there. In England every part of our chalk is completely covered by vegetable soil, which although very thin on many parts of our downs or smooth hills, yet affords support to peculiar grasses and other vegetables, on which are pastured vast quantities of sheep. The chalk of Franco is said to contain 11 per cent. of magnesia, to which the barrenness may be owing.
9. On the authority of Mr. Parkinson I notice that the supposition of having discovered a specimen of Trigonia in chalk is erroneous. This belongs only to inferior strata.
10. See the paper on this subject, by Sir Henry Englefield, in the Transactions of the Linnean Society.
11. Hence the country on the northern side of London is so thinly inhabited.
12. One of these prodigious falls of the chalk cliffs, which make a residence near them frequently so dangerous, occurred a few days before my visiting this spot, accompanied by a remarkable circumstance. The clergyman of East Dean, who was walking near the brink of the precipice, perceived the ground to give way under him, and had the presence of mind to escape over the rent that was forming at some distance from the edge of the cliff. In a few seconds, the mass of chalk which he had stood on, to the extent of 300 feet in length, and 70 or 80 in breadth, fell with a tremendous crash. In going from Newhaven round Beachy Head, under the cliff at low water, I passed over these ruins, which were truly terrific, and observed that their fall had been occasioned by the sea acting on the chalk marl, and thus undermining the chalk; the former from the dip of the strata, just begins to appear at the bottom of the cliff at this spot. It may be proper to mention that this place is highly deserving to he visited, on account of the fossils to be seen in the chalk and green sand; among these I remarked many large madrepores, and some very large and entire shells of the fibrous kind, the fragments of which are so numerous in the chalk.
13. It will be an interesting investigation for the experienced botanist to trace the living analogues of these ancient productions of this part of the earth. Such of them as have been recognised are found to belong to species now growing only in the torrid zone; thus adding to the evidence afforded by the animal remains of the great change that must have taken place in the climate.
14. The only shells which I noticed thus alternating with those of freshwater, appeared to belong to the genus Cerithium, but not having specimens of them it has since occurred to me, and it will deserve future observation, whether these were not the Potamides Lamarkii. They are abundant at Gurnet Point.
15. Since the reading of this paper I have been favoured by the Rev. William Buckland, Prof. of Mineralogy, Oxford, with specimens of freshwater shells which he has collected at Hordwell cliff. They consist of the lymneus, planorbis, cyclostoma, and a bivalve resembling a freshwater mytilus. From the state of the fossils, and the nature of the stratum in which they were imbedded, they would appear to belong to the lower freshwater formation.
16. It is not a little singular that some of the smaller upright stones of Stonehenge consist of a sort of greenstone, and must therefore have been brought from very great distance, no such rock occurring in the neighbourhood.
17. Specimens of these collected in the neighbourhood of High Wycombe, by the Hon. Henry Grey Bennett, Pres. G. S. are deposited in the Museum of the Society.
18. These were found in some specimens of clay containing also freshwater shells which were dug out of a deep well at Newport. But as no distinct account was kept of the strata passed through, it is not certain to which of the freshwater formations they belong.
19. It is proper to observe that the Potamides of Lamarck is a Cerithium. But having considered the cerithia as marine shells, he thought it proper, on finding a species among the freshwater shells, to regard this as of a distinct genus; founding the distinction not on any difference in its form, but on the difference of the water in which it had lived.
20. The Egyptian pebbles are said to occur in a similar situation.
21. A very fine example of one occurs in a specimen in the museum of the Geological Society, presented by Leonard Horner, Esq. It is a small bivalve resembling a pecten.

Errata

1. Original: 9 was amended to 11: detail
2. Original: found was amended to formed: detail
3. Original: has was amended to have: detail
4. Original: petrefactions was amended to petrifactions: detail
5. Original: was amended to ;: detail
6. Original: may was amended to might: detail