Geological Evidences of the Antiquity of Man/Chapter 12
CHAPTER XII.
ANTIQUITY OF MAN RELATIVELY TO THE GLACIAL PERIOD AND TO THE EXISTING FAUNA AND FLORA.
CHRONOLOGICAL RELATION OF THE GLACIAL PERIOD, AND THE EARLIEST KNOWN SIGNS OF MAN'S APPEARANCE IN EUROPE—SERIES OF TERTIARY DEPOSITS IN NORFOLK AND SUFFOLK IMMEDIATELY ANTECEDENT TO THE GLACIAL PERIOD—GRADUAL REFRIGERATION OF CLIMATE PROVED BY THE MARINE SHELLS OF SUCCESSIVE GROUPS—MARINE NEWER PLIOCENE SHELLS OF NORTHERN CHARACTER, NEAR WOODBRIDGE—SECTION OF THE NORFOLK CLIFFS—NORWICH CRAG FOREST BED AND FLUVIO-MARINE STRATA—FOSSIL PLANTS AND MAMMALIA OF THE SAME—OVERLYING BOULDER CLAY AND CONTORTED DRIFT—NEWER FRESHWATER FORMATION OF MUNDESLEY COMPARED TO THAT OF HOXNE—GREAT OSCILLATIONS OF LEVEL IMPLIED BY THE SERIES OF STRATA IN THE NORFOLK CLIFFS—EARLIEST KNOWN DATE OF MAN LONG SUBSEQUENT TO THE EXISTING FAUNA AND FLORA.
FREQUENT allusions have been made in the preceding pages to a period called the glacial, to which no reference is made in the Chronological Table of Formations given at p. 7. It comprises a long series of ages, chiefly of post-tertiary date, during which the power of cold, whether exerted by glaciers on the land, or by floating ice on the sea, was greater in the northern hemisphere, and extended to more southern latitudes than now.
It often happens that when in any given region we have pushed back our geological investigations as far as we can, in search of evidence of the first appearance of man in Europe, we are stopped by arriving at what is called the 'boulder clay' or 'northern drift.' This formation is usually quite destitute of organic remains, so that the thread of our inquiry into the history of the animate creation, as well as of man, is abruptly cut short. The interruption, however, is by no means encountered at the same point of time in every district. In the case of the Danish peat, for example, we get no farther back than the recent period of our Chronological Table (p. 7), and then meet with the boulder clay; and it is the same in the valley of the Clyde, where the marine strata contain the ancient canoes before described (p. 47), and where nothing intervenes between that recent formation and the glacial drift. But we have seen that, in the neighbourhood of Bedford (p. 155), the memorials of man can be traced much farther back into the past, namely, into the post-pliocene epoch, when the human race was contemporary with the mammoth and many other species of mammalia now extinct. Nevertheless, in Bedfordshire as in Denmark, the formation next antecedent in date to that containing the human implements is still a member of the glacial drift, with its erratic blocks.
If the reader remembers what was stated in the Eighth Chapter, p. 144, as to the absence or extreme scarcity of human bones and works of art in all strata, whether marine or fresh-water, even in those formed in the immediate proximity of land inhabited by millions of human beings, he will be prepared for the general dearth of human memorials in glacial formations, whether recent, post-pliocene, or of more ancient date. If there were a few wanderers over lands covered with glaciers, or over seas infested with ice-bergs, and if a few of them left their bones or weapons in moraines or in marine drift, the chances, after the lapse of thousands of years, of a geologist meeting with one of them must be infinitesimally small.
It is natural, therefore, to encounter a gap in the regular sequence of geological monuments bearing on the past history of man, wherever we have proofs of glacial action having prevailed with intensity, as it has done over large parts of Europe and North America, in the post-pliocene period. As we advance into more southern latitudes approaching the 50th parallel of latitude in Europe, and the 40th in North America, this disturbing cause ceases to oppose a bar to our inquiries; but even then, in consequence of the fragmentary nature of all geological annals, our progress is inevitably slow in constructing any thing like a connected chain of history, which can only be effected by bringing the links of the chain found in one area to supply the information which is wanting in another.
The least interrupted series of consecutive documents to which we can refer in the British Islands, when we desire to connect the tertiary with the post-tertiary periods, are found in the counties of Norfolk, Suffolk, and Essex; and I shall speak of them in this chapter, as they have a direct bearing on the relations of the human and glacial periods, which will be the subject of several of the following chapters. The fossil shells of the deposits in question clearly point to a gradual refrigeration of climate, from a temperature some what warmer than that now prevailing in our latitudes to one of intense cold; and the successive steps which have marked the coming on of the increasing cold are matters of no small geological interest.
It will be seen in the Table at p. 7, that next before the post-tertiary period stands the pliocene, divided into the older and newer. The shelly and sandy beds representing these periods in Norfolk and Suffolk are termed provincially Crag, having under that name been long used in agriculture to fertilise soils deficient in calcareous matter, or to render them less stiff and impervious. In Suffolk, the older pliocene strata called Crag are divisible into the Coralline and the Red Crags, the former being the older of the two. In Norfolk, a more modern formation, commonly termed the 'Norwich,' or sometimes the 'mammaliferous' Crag, which is referable to the newer pliocene period, occupies large areas.
We are indebted to Mr. Searles Wood, F.G.S., for an admirable monograph on the fossil shells of these British pliocene formations. He has not himself given us an analysis of the results of his treatise, but the following tables have been drawn up for me by Mr. S. P. Woodward, the well-known author of the 'Manual of the Mollusca, Recent and Fossil' (London, 1853–6), in order to illustrate some of the general conclusions to which Mr. Wood's careful examination of 442 species of mollusca has led.
- Brachiopoda
6
- Conchifera
206
- Gasteropoda
230
- Total
42
Distribution of the above Marine Testacea.
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Number of Species.
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Species common to the
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Proportion of Recent to Extinct Species.
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Recent.
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Extinct
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Per-centage of
Recent.
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Recent Species not living now in British Seas.
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Northern Species.
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Southern.
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By far the greater number of the recent marine species included in these tables are still inhabitants of the British seas; but even these differ considerably in their relative abundance, some of the commonest of the Crag shells being now extremely scarce; as, for example, Buccinum Dalei, and others, rarely met with in a fossil state, being now very common, as Murex erinaceus and Cardium echinatum.
The last table throws light on a marked alteration in the climate of the three successive periods. It will be seen that in the Coralline Crag there are twenty-seven southern shells, including twenty-six Mediterranean, and one West Indian species (Erato Maugeriæ). Of these only thirteen occur in the Red Crag, associated with three new southern species, while the whole of them disappear from the Norwich beds. On the other hand, the Coralline Crag contains only two arctic shells, Admete viridula and Limopsis pygmæa; whereas the Red Crag contains, as stated in the table, eight northern species, all of which recur in the Norwich Crag, with the addition of four others, also inhabitants of the arctic regions; so that there is good evidence of a continual refrigeration of climate during the pliocene period in Britain. The presence of these northern shells cannot be explained away by supposing that they were inhabitants of the deep parts of the sea; for some of them, such as Tellina calcarea and Astarte borealis, occur plentifully, and sometimes with the valves united by their ligament, in company with other littoral shells, such as Mya arenaria and Littorina rudis, and evidently not thrown up from deep water. Yet the northern character of the Norwich Crag is not fully shown by simply saying that it contains twelve northern species, now no longer found in British seas, since several boreal shells which still linger in the Scottish deeps do not abound there as they did in the latter days of the Crag period. It is the predominance of certain genera and species which satisfies the mind of a conchologist as to the arctic character of the Norwich Crag. In like manner, it is the presence of such genera as Pyrula, Columbella, Terebra, Cassidaria, Pholadomya, Lingula, Discina, and others which give a southern aspect to the Coralline Crag shells.
The cold, which had gone on increasing from the time of the Coralline to that of the Norwich Crag, continued, though not perhaps without some oscillations of temperature, to become more and more severe after the accumulation of the Norwich Crag, until it reached its maximum in what has been called the glacial epoch. The marine fauna of this last period contains, both in Ireland and Scotland, recent species of mollusca now living in Greenland and other seas far north of the areas where we find their remains in a fossil state.
The refrigeration of climate from the time of the older to that of the newer Pliocene strata is not now announced for the first time, as it was inferred from a study of the Crag shells in 1846 by the late Edward Forbes.[2]
The most southern point to which the marine beds of the Norwich Crag have yet been traced is at Chillesford, near Woodbridge, in Suffolk, about eighty miles north-east of London, where, as Messrs. Prestwich and Searles Wood have pointed out,[3] they exhibit decided marks of having been deposited in a sea of a much lower temperature than that now prevailing in the same latitude. Out of twenty-three shells obtained in that locality from argillaceous strata twenty feet thick, two only, namely, Nucula Cobboldiæ and Tellina obliqua, are extinct, and not a few of the other species, such as Leda arctica, Cardium groenlandicum, Lucina borealis, Cyprina islandica, Panopæa norvegica, and Mya truncata, betray a northern, and some of them an arctic character.
These Chillesford beds are supposed to be somewhat more modern than any of the purely marine strata of the Norwich Crag exhibited by the sections of the Norfolk cliffs NW. of Cromer, which I am about to describe. Yet they probably preceded in date the 'Forest Bed' and fluvio-marine deposits of those same cliffs. They are, therefore, of no small importance in reference to the chronology of the glacial period, since they afford evidence of an assemblage of fossil shells with a proportion of between eight and nine in a hundred of extinct species occurring so far south as lat. 53º N., and indicating so cold a climate as to imply that the glacial period commenced before the close of the newer pliocene era.
The annexed section will give a general idea of the ordinary succession of the newer pliocene and post-pliocene strata which rest upon the chalk in the Norfolk and Suffolk cliffs. These cliffs vary in height from fifty to above three hundred feet. At the north-western extremity of the section at Weybourne (beyond the limits of the annexed diagram), and from thence to Cromer, a distance of seven miles, the Norwich crag, a marine deposit, reposes immediately upon the chalk. A vast majority of its shells are of living species now inhabiting the British seas, such as Cardium edule, Cyprina islandica, and Scalaria groenlandica, and some few extinct, as Fusus striatus, Tellina obliqua, and Nucula Cobboldiæ. At Cromer jetty this formation thins out, as expressed in the diagram at a; and to the south we find No. 3, or what is commonly called the 'Forest Bed,' reposing immediately upon the chalk, and occupying as it were the place previously held by the marine crag No. 2. Fig. 27
DIAGRAM TO ILLUSTRATE THE GENERAL SUCCESSION OF THE STRATA IN THE NORFOLK CLIFFS, EXTENDING SEVERAL MILES N.W. AND S.E. OF CROMER.
1 Upper chalk with flints in regular stratification.
2 Norwich Crag, rising from low water at Cromer, to the top of the cliffs at Weybourne, seven miles distant.
3 'Foresr Bed,' with stumps of trees in situ and remains of Elphas meridionalis, Rhinocerus Etruscus, &c. This bed increases in depth and thickness eastward. No crag (No. 2) known east of Cromer Jetty.
3′ Fluvio-marine series. At Cromer and eastward, with abundant lignite beds and mammalian remains, and with cones of the scotch and spruce firs and wood. At Runton, north-west of Cromer, expanding into a thick freshwater deposit, with overlying marine strata, elsewhere consisting of alternating sands and clays, tranquilly deposited, some with marine, others with freshwater shells.
4 Boulder clay of glacial period, with far transported erratics, some of them polished and scratched, twenty to eighty feet in thickness.
5 Contorted drift.
6 Superficial gravel and sand with covering of vegetable soil.As the sea is always gaining on the land, new sets of trees are brought to light from time to time, so that the breadth as well as length of the area of ancient forest land seems to have been considerable. Next above No. 2, we find a series of sands and clays with lignite (No. 3'), sometimes ten feet thick, and containing alternations of fluviatile and marine strata, implying that the old forest land, which may at first have been considerably elevated above the level of the sea, had sunk down so as to be occasionally overflowed by a river, and at other times by the salt waters of an estuary. There were probably several oscillations of level which assisted in bringing about these changes, during which trees were often uprooted and laid prostrate, giving rise to layers of lignite. Occasionally marshes were formed and peaty matter accumulated, after which salt water again predominated, so that species of Mytilus, Mya, Leda, and other marine genera, lived in the same area where the Unio, Cyclas, and Paludina had nourished for a time. That the marine shells lived and died on the spot, and were not thrown up by the waves during a storm, is proved, as Mr. King has remarked, by the fact that at West Runton, NW. of Cromer, the Mya truncata and Leda myalis are found with both valves united and erect in the loam, all with their posterior or siphuncular extremities uppermost. This attitude affords as good evidence to the conchologist that those mollusca lived and died on the spot as the upright position of the trees proves to the botanist that there was a forest over the chalk east of Cromer.
Between the stumps of the buried forest, and in the lignite above them, are many well-preserved cones of the Scotch and spruce firs, Pinus sylvestris, and Pinus Abies. The specific names of these fossils were determined for me in 1840, by a botanist of no less authority than the late Robert Brown; and Professor Heer has lately examined a large collection from the same stratum, and recognised among the cones of the spruce some which had only the central part or axis remaining, the rest having been bitten off, precisely in the same manner as when in our woods the squirrel has been feeding on the seeds. There is also in the forest-bed a great quantity of resin in lumps, resembling that gathered for use, according to Professor Heer, in Switzerland, from beneath spruce firs.
The following is a list of some of the plants which were collected by the Rev. S. G. King, in 1861, from the forest bed, and named by Professor Heer:—
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Mundesley. | |
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Mundesley. | |
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Bacton. | |
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" |
The insects, so far as they are known, including several species of Donacea, are, like the plants and freshwater shells, of living species. It may be remarked, however, that the Scotch fir has been confined in historical times to the northern parts of the British isles, and the spruce fir is nowhere indigenous in Great Britain. The other plants are such as might now be found in Norfolk, and many of them indicate fenny or marshy ground.
When we consider the familiar aspect of the flora, the accompanying mammalia are certainly most extraordinary. There are no less than two elephants, a rhinoceros and hippopotamus, a large extinct beaver, and several large estuarian and marine mammalia, such as the walrus, the narwhal, and the whale.
The following is a list of some of the species of which the bones have been collected by Messrs. Gunn and King, and named by Dr. Falconer and other geologists:—
Mammalia of the Forest and Lignite Beds below the Glacial Drift of the Norfolk Cliffs.
- Elephas meridionalis.
- Elephas primigenius var.
- Elephas antiquus.
- Rhinoceros etruscus.
- Hippopotamus (major?).
- Sus.
- Equus (fossilis?).
- Bos.
- Cervus Capreolus? and other species of Cervus.
- Arvicola amphibia.
- Castor trogontherium.
- Castor europæus.
- Narwhal, walrus, and large whale, or Balænoptera?
Mr. Gunn informs me that two large whales were found in the fluvio-marine beds at Bacton, and that the vertebræ of one of them, shown to Professor Owen, were said by him to imply that the animal was sixty feet long. A narwhal's tusk was discovered by Mr. King near Cromer, and the remains of a walrus. No less than three species of elephant, as determined by Dr. Falconer, have been obtained from the strata 3 and 3', of which, according to Mr. King, E. meridionalis is the most common, the mammoth next in abundance, and the third, E. antiquus, comparatively rare.
The freshwater shells accompanying the fossil quadrupeds, above enumerated, are such as now inhabit rivers and ponds in England; but among them, as at Runton, between the 'forest bed' and the glacial deposits, a remarkable variety of the Cyclas amnica occurs, fig. 28, p. 218, identical with that which accompanies the Elephas antiquus at Ilford and Grays in the valley of the Thames.
All the freshwater shells of the beds intervening between the forest-bed No. 3, and the glacial formation 4, fig. 27, are of recent species. As to the small number of marine shells occurring in the same fluvio-marine series, I have seen none which belonged to extinct species, although one or two have been cited by authors. I am in doubt, therefore, whether to class the forest bed and overlying strata as post-pliocene, or to consider them as beds of passage between the newer pliocene and post-pliocene periods. The fluvio-marine series usually terminates upwards in finely laminated sands and clays without fossils, on which reposes the boulder clay.
Fig. 28
Cyclas (Pisidium) amnica var.?
The two middle figures are of the natural size.
This formation, No. 4, is of very varying thickness. Its glacial character is shown, not only by the absence of stratification, and the great size and angularity of some of the included blocks of distant origin, but also by the polished and scratched surfaces of such of them as are hard enough to retain any markings.
Near Cromer, blocks of granite from six to eight feet in diameter have been met with, and smaller ones of sienite, porphyry, and trap, besides the wreck of the London clay, chalk, oolite, and lias, mixed with more ancient fossiliferous rocks. Erratics of Scandinavian origin occur chiefly in the lower portions of the till. I came to the conclusion in 1834, that they had really come from Norway and Sweden, after having in that year traced the course of a continuous stream of such blocks from those countries to Denmark, and across the Elbe, through Westphalia, to the borders of Holland. It is not surprising that they should then reappear on our eastern coast between the Tweed and the Thames, regions not half so remote from parts of Norway as are many Russian erratics from the sources whence they came.
According to the observations of the Rev. J. Gunn and the late Mr. Trimmer, the glacial drift in the cliffs at Lowestoff consists of two divisions, the lower of which abounds in the Scandinavian blocks, supposed to have come from the north-east; while the upper, probably brought by a current from the north-west, contains chiefly fragments of oolitic rocks, more rolled than those of the lower deposit. The united thickness of the two divisions without reckoning some interposed laminated beds, is eighty feet, but it probably exceeds one hundred feet near Happisburgh.[4] Although these subdivisions of the drift may be only of local importance, they help to show the changes of currents and other conditions, and the great lapse of time which the accumulation of so varied a series of deposits must have required.
The lowest part of the glacial till, resting on the laminated clays before mentioned, is very even and regular, while its upper surface is remarkable for the unevenness of its outline, owing partly, in all likelihood, to denudation, but still more to other causes presently to be discussed.
The overlying strata of sand and gravel, No. 5, p. 213, often display a most singular derangement in their stratification, which in many places seems to have a very intimate relation to the irregularities of outline in the subjacent till. There are some cases, however, where the upper strata are much bent, while the lower beds of the same series have continued horizontal. Thus the annexed section (fig. 29) represents a cliff about fifty feet high, at the bottom of which is till, or unstratified clay, containing boulders, having an even horizontal surface, on which repose conformably beds of laminated clay and sand about five feet thick, which, in their turn, are succeeded by vertical, bent, and contorted layers of sand and loam twenty feet thick, the whole being covered by flint gravel. The curves of the variously coloured beds of loose sand, loam, and pebbles, are so complicated that not only may we sometimes find portions of them which maintain
Fig. 29
Cliff 50 feet high between Bacton Gap and Mundesley.
their verticality to a height of ten or fifteen feet, but they have also been folded upon themselves in such a manner that continuous layers might be thrice pierced in one perpendicular boring.
At some points there is an apparent folding of the beds round a central nucleus, as at a, fig. 30, where the strata seem
Fig. 30
Folding of the strata between East and West Runton. |
Fig. 31
Section of concentric beds west of Cromer. |
bent round a small mass of chalk, or, as in fig. 31, where the blue clay, No. 1, is in the centre; and where the other strata, 2, 3, 4, 5, are coiled round it; the entire mass being twenty feet in perpendicular height. This appearance of concentric arrangement around a nucleus is, nevertheless, delusive, being produced by the intersection of beds bent into a convex shape; and that which seems the nucleus being, in fact, the innermost bed of the series, which has become partially visible by the removal of the protuberant portions of the outer layers.
To the north of Cromer are other fine illustrations of contorted drift reposing on a floor of chalk horizontally stratified and having a level surface. These phenomena, in themselves sufficiently difficult of explanation, are rendered still more anomalous by the occasional inclosure in the drift of huge fragments of chalk many yards in diameter. One striking instance occurs west of Sherringham, where an enormous pinnacle of chalk, between seventy and eighty feet in height, is flanked on both sides by vertical layers of loam, clay, and gravel (fig. 32).
Fig. 32
Included pinnacle of chalk at Old Hythe point, west of Sherringham.
This chalky fragment is only one of many detached masses
which have been included in the drift, and forced along with it into their present position. The level surface of the chalk in situ (d) may be traced for miles along the coast, where it has escaped the violent movements to which the incumbent drift has been exposed.[5]
We are called upon, then, to explain how any force can have been exerted against the upper masses, so as to produce movements in which the subjacent strata have not participated. It may be answered that, if we conceive the till and its boulders to have been drifted to their present place by ice, the lateral pressure may have been supplied by the stranding of ice-islands. We learn, from the observations of Messrs. Dease and Simpson in the polar regions, that such islands, when they run aground, push before them large mounds of shingle and sand. It is therefore probable that they often cause great alterations in the arrangement of pliant and incoherent strata forming the upper part of shoals or submerged banks, the inferior portions of the same remaining unmoved. Or many of the complicated curvatures of these layers of loose sand and gravel may have been due to another cause, the melting on the spot of icebergs and coast ice in which successive deposits of pebbles, sand, ice, snow, and mud, together with huge masses of rock fallen from cliffs, may have become interstratified. Ice-islands so constituted often capsize when afloat, and gravel once horizontal may have assumed, before the associated ice was melted, an inclined or vertical position. The packing of ice forced up on a coast may lead to a similar derangement in a frozen conglomerate of sand or shingle, and, as Mr. Trimmer has suggested,[6] alternate layers of earthy matter may have sunk down slowly during the liquefaction of the intercalated ice so as to assume the most fantastic and anomalous positions, while the strata below, and those afterwards thrown down above, may be perfectly horizontal (see above).
In most cases where the principal contortions of the layers of gravel and sand have a decided correspondence with deep indentations in the underlying till, the hypothesis of the melting of large lumps and masses of ice once mixed up with the till affords the most natural explanation of the phenomena. The quantity of ice now seen in the cliffs near Behring's Straits, in which the remains of fossil elephants are common, and the huge fragments of solid ice which Meyendorf discovered in Siberia, after piercing through a considerable thickness of incumbent soil, free from ice, is in favour of such an hypothesis, the partial failure of support necessarily giving rise to foldings in the overlying and previously horizontal layers, as in the case of creeps in coal mines.[7]
In the diagram of the cliffs at p. 213, the bent and contorted beds No. 5, last alluded to, are represented as covered by undisturbed beds of gravel and sand, No. 6. These are usually destitute of organic remains; but at some points marine shells of recent species are said to have been found in them. They afford evidence at many points of repeated denudation and redeposition, and may be the monuments of a long series of ages.
Mundesley Post-glacial Freshwater Formation.
In the range of cliffs above described at Mundesley, about two miles south-east of Cromer, a fine example is seen of a freshwater formation, newer than all those already mentioned, a deposit which has filled up a depression hollowed out of all the older beds 3, 4, and 5, of the section, p. 213. When I examined this line of coast in 1839, the section alluded to was not so clearly laid open to view as it has been of late years, and finding at that period not a few of the fossils in the lignite beds, No. 3′, above the forest bed, identical in species with those from the post-glacial deposits, b c, I supposed the whole to have been of contemporaneous origin, and so described them in my paper on the Norfolk cliffs.[8]
Fig. 33
Section of the newer freshwater formation in the cliffs at Mundesley, two miles SE. of Cromer, drawn up by the Rev. S. W. King.
Height of cliff where lowest, 35 feet above high water.
Older Series.
3 Forest bed, with elephant, rhinoceros, stag, &c., and with tree roots and stumps, also below the beach line.
3′ Finely laminated sands and clays, with thin layer of lignite, and shells of Cyclas, and Valvata, and with Mytilus in some beds.
4 Glacial boulder till.
5 Contorted drift.
6 Gravel overlying contorted drift.N.B.—No. 2 of the section, fig. 27, at p. 213, is wanting here.
Newer Freshwater Beds.
b Black peaty deposit, with shells of Anodon, Valvata, Cyclas, Succinea, Limnea, Paludina, &c., seeds of Ceratophyllum demersum, Nuphar lutea, scales and bones of pike, perch, salmon, &c., elytra of Donacia, Copris, Harpalus, and other beetles.
c Yellow sands.
d Drift gravel.Mr. Gunn was the first to perceive this mistake, which he explained to me on the spot when I revisited Mundesley in the autumn of 1859, in company with Dr. Hooker and Mr. King. The last-named geologist has had the kindness to draw up for me the annexed diagram of the various beds which he has recently studied in detail.[9]
The formations 3, 4, and 5, already described, p. 213, were evidently once continuous, for they may be followed for miles NW. and SE. without a break, and always in the same order. A valley or river channel was cut through them, probably during the gradual upheaval of the country, and the hollow became afterwards the receptacle of the comparatively modern freshwater beds, a, b, c, and d. They may well represent a silted up river-channel, which remained for a time in the state of a lake or mere, and in which the black peaty mass, b, accumulated by a very slow growth over the gravel of the river-bed a. In b, we find remains of some of the same plants which were enumerated as common in the ancient lignite in 3′, such as the yellow water-lily and pond-wort, together with some fresh water shells which occur in the same fluvio-marine series 3′.
Fig. 34
Paludina marginata Michaud. (P. minuta Strickland.)
Hydrobia marginata.[10]
The middle figure is of the natural size.
The only shell which I found not referable to a British species is the minute paludina, fig. 34, already alluded to, p. 164.
When I showed the scales and teeth of the pike, perch, roach, and salmon, which I obtained from this formation, to Mr. Agassiz, he thought they varied so much from their nearest living representatives that they might rank as distinct species; but Mr. Yarrell doubted the propriety of so distinguishing them. The insects, like the shells and plants, are identical, so far as they are known, with living British species. No progress has yet been made at Mundesley in discovering the contemporary mammalia.
By referring to the description and section of the freshwater deposit at p. 159, the reader will at once perceive the striking analogy of the Mundesley and Hoxne deposits, the latter so productive of flint implements of the Amiens type. Both of them, like the Bedford gravel with flint tools and the bones of extinct mammalia (noticed at p. 164), are postglacial. It will also be seen that a long series of events, accompanied by changes in physical geography, intervened between the 'forest bed,' No. 3, fig. 27, p. 213, when the Elephas meridionalis flourished, and the period of the Mundesley fluviatile beds a, b, c; just as in France I have shown, p. 199, that the same E. meridionalis belonged to a system of drainage different from and anterior to that with which the flint implements of the old alluvium of the Somme and the Seine were connected.
Before the growth of the ancient forest, No. 3, fig. 33, the Mastodon arvernensis, a large proboscidian, characteristic of the Norwich crag, appears to have died out, or to have become scarce, as no remains of it have yet been found in the Norfolk cliffs. There was, no doubt, time for other modifications in the mammalian fauna between the era of the marine beds, No. 2, p. 213 (the shells of which imply permanent submergence beneath the sea), and the accumulation of the uppermost of the fluvio-marine, and lignite beds, No. 3', which overlie both Nos. 3 and 2, or the buried forest and the crag. In the interval we must suppose repeated oscillations of level, during which land covered with trees, an estuary with its freshwater shells, and the sea with its Mya truncata and other mollusca still retaining their erect position, gained by turns the ascendency. These changes were accompanied by some denudation followed by a grand submergence of several hundred feet, probably brought about slowly, and when floating ice aided in transporting erratic blocks from great distances. The glacial till, No. 4, then originated, and the gravel and sands, No. 5, were afterwards superimposed on the boulder clay, first in horizontal beds, which became subsequently contorted. These were covered in their turn by other layers of gravel and sand, No. 6, pp. 213 and 224, the downward movement still continuing.
The entire thickness of the beds above the chalk at some points near the coast, and the height at which they now are raised, are such as to show that the subsidence of the country after the growth of the forest bed, exceeded four hundred feet. The re-elevation must have amounted to nearly as many feet, as the site of the ancient forest, originally subaërial, has been brought up again to within a few feet of high-water mark. Lastly, after all these events, and probably during the final process of emergence, the valley was scooped out in which the newer freshwater strata of Mundesley, fig. 33, p. 224, were gradually deposited.
Throughout the whole of this succession of geographical changes, the flora and invertebrate fauna of Europe appear to have undergone no important revolution in their specific characters. The plants of the forest bed belonged already to what has been called the Germanic flora. The mollusca, the insects, and even some of the mammalia, such as the European beaver and roebuck, were the same as those now coexisting with man. Yet the oldest memorials of our species at present discovered in Great Britain are post-glacial, or posterior in date to the boulder clay, No. 4, pp. 213 and 224. The position of the Hoxne flint implements corresponds with that of the Mundesley beds, from a to d, p. 224, and the most likely stratum in which to find hereafter flint tools is no doubt the gravel a of that section which has all the appearance of an old river-bed. No flint tools have yet been observed there, but had the old alluvium of Amiens or Abbeville occurred in the Norfolk cliffs instead of the Valley of the Somme, and had we depended on the waves of the sea instead of the labour of many hundred workmen continued for twenty years, for exposing the flint implements to view, we might have remained ignorant to this day of the fossil relics brought to light by M. Boucher de Perthes, and those who have followed up his researches.
Neither need we despair of one day meeting with the signs of man's existence in the forest bed No. 3, or in the overlying strata 3', on the ground of any uncongeniality in the climate or incongruity in the state of the animate creation with the well-being of our species. For the present we must be content to wait and consider that we have made no investigations which entitle us to wonder that the bones or stone weapons of the era of the Elephas meridionalis have failed to come to light. If any such lie hid in those strata, and should hereafter be revealed to us, they would carry back the antiquity of man to a distance of time probably more than twice as great as that which separates our era from that of the most ancient of the tool-bearing gravels yet discovered in Picardy, or elsewhere. But even then the reader will perceive that the age of man, though preglacial, would be so modern in the great geological calendar, as given at p. 7, that he would scarcely date so far back as the commencement of the post-pliocene period.
- ↑ These 19 species must be added to the numbers 33, 4, and 116 respectively in order to obtain the full amount of common species in each of those cases.
- ↑ Manual of Geological Survey, London, 1846, p. 391.
- ↑ Quarterly Geological Journal, 1849, vol. v. p. 345.
- ↑ Quarterly Geological Journal, vol. vii. p. 21.
- ↑ For a full account of the drift of East Norfolk, see a paper by the author, Philosophical Magazine, No. 104, May, 1840.
- ↑ Quarterly Journal, Geological Society, vol. vii. pp. 22, 30.
- ↑ See Manual of Geology, by the author, p. 51.
- ↑ Philosophical Magazine, vol. xvi. May 1840, p. 345.
- ↑ Mr. Prestwich has given a correct account of this section in a paper read to the British Association, Oxford, 1860. See Geologist's Magazine, vol. iv. 1861.
- ↑ This shell is said to have a subspiral operculum (not a concentric one, as in Paludina), and therefore to be referable to the Hydrobia, a subgenus of Rissoa. But this species is always associated with freshwater shells, while the Rissoæ frequent marine and brackish waters.