The Antiquity of Man/Chapter 12
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 above (Chapter 1). It comprises a long series of ages, 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 Chronologic Table, 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 (Chapter 3), and where nothing intervenes between that Recent formation and the glacial drift. But we have seen that, in the neighbourhood of Bedford the memorials of Man can be traced much farther back into the past, namely, into the Pleistocene 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 as to the absence or extreme scarcity of human bones and works of art in all strata, whether marine or freshwater, 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, Pleistocene, 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 Pleistocene 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 anything 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 Pliocene with the Pleistocene 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 somewhat 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 Chronological Table, that next before the Pleistocene period stands the Pliocene. The shelly and sandy beds representing these periods in Norfolk and Suffolk are termed provincially Crag, having under the 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 Mollusca, Recent and Fossil" (London 1851-56), in order to illustrate some of the general conclusions to which Mr. Wood's careful examination of 442 species of mollusca has led.
TABLE 12/1. NUMBER OF KNOWN SPECIES OF MARINE TESTACEA IN THE THREE
ENGLISH PLIOCENE DEPOSITS, CALLED THE NORWICH, THE RED, AND THE
COLUMN 1 : NAME.
COLUMN 2 : NUMBER.
Brachiopoda : 6.
Lamellibranchia : 206.
Gasteropoda : 230.
TOTAL : 442.
TABLE 12/2. DISTRIBUTION OF THE ABOVE MARINE TESTACEA.
COLUMN 1 : NAME.
COLUMN 2 : NUMBER.
Norwich Crag : 81.
Red Crag : 225.
Coralline Crag : 327.
Species common to the Norwich and Red Crag (not in Coralline) : 33.
Species common to the Norwich and Coralline (not in Red) : 4.
Species common to the Red and Coralline (not in Norwich) : 116.
Species common to the Norwich, Red, and Coralline : 19.
[Preceding table, last line]
TABLE 12/3. PROPORTION OF RECENT TO EXTINCT SPECIES.
COLUMN 1 : NAME.
COLUMN 2 : NUMBER OF RECENT.
COLUMN 3 : NUMBER OF EXTINCT.
COLUMN 4 : PERCENTAGE OF RECENT.
Norwich Crag : 69 : 12 : 85%.
Red Crag : 130 : 95 : 57%.
Coralline Crag : 168 : 159 : 51%.
TABLE 12/4. RECENT SPECIES NOT LIVING NOW IN BRITISH SEAS.
COLUMN 1 : NAME.
COLUMN 2 : NUMBER OF NORTHERN.
COLUMN 3 : NUMBER OF SOUTHERN.
Norwich Crag : 12 : 0.
Red Crag : 8 : 16.
Coralline Crag : 2 : 27.
In the above list I have not included the shells of the glacial beds of the Clyde and of several other British deposits of newer origin than the Norwich Crag, in which nearly all—perhaps all—the species are Recent. The land and freshwater shells, thirty-two in number, have also been purposely omitted, as well as three species of London Clay shells, suspected by Mr. Wood himself to be spurious.
By far the greater number of the living 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, Buccinopsis 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 Maugeriae). 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 shells closely related to arctic forms of the genera Admete and Limopsis. 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. It is the predominance of certain genera and species, such as Tellina calcarea, Astarte borealis, Scalaria groenlandica, and Fusus carinatus, 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.
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 80 miles north-east of London, where, as Messrs. Prestwich and Searles Wood have pointed out, 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 20 feet thick, two only, namely, Nucula Cobboldiae and Tellina obliqua, are extinct, and not a few of the other species, such as Leda lanceolata, Cardium groenlandicum, Lucina borealis, Cyprina islandica, Panopaea 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 north-west 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 latitude 53 degrees north, and indicating so cold a climate as to imply that the glacial period commenced before the close of the Pliocene era.
(FIGURE 27. [omitted] DIAGRAM TO ILLUSTRATE THE GENERAL SUCCESSION OF THE STRATA IN THE NORFOLK CLIFFS, EXTENDING SEVERAL MILES NORTH-WEST AND SOUTH-EAST OF CROMER.
- A. Site of Cromer Jetty.
- 1. Upper Chalk with flints in regular stratification.
- 2. Norwich Crag, rising from low water at Cromer to the top of the cliffs at Weybourn, seven miles distant.
- 3. "Forest Bed," with stumps of trees in situ and remains of Elephas meridionalis, E. primigenius, E. antiquus, Rhinoceros etruscus, etc. This bed increases in depth and thickness eastward. No Crag (Number 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, 20 to 80 feet in thickness.
- 5. Contorted drift.
- 6. Superficial gravel and sand with covering of vegetable soil.)
The annexed section (Figure 27) will give a general idea of the ordinary succession of the Pliocene and Pleistocene 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 Weybourn (beyond the limits of the annexed diagram), and from thence to Cromer, a distance of 7 miles, the Norwich Crag, a marine deposit, reposes immediately upon the Chalk. A vast majority of its shells are of living species such as Cardium edule, Cyprina islandica, Scalaria groenlandica, and Fusus antiquus, and some few extinct, as Tellina obliqua, and Nucula Cobboldiae. At Cromer jetty this formation thins out, as expressed in the diagram at A; and to the south we find Number 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 Number 2. This buried forest has been traced for more than 40 miles, being exposed at certain seasons and states of the beach between high and low water mark. It extends from Cromer to near Kessingland, and consists of the stumps of numerous trees standing erect, with their roots attached to them, and penetrating in all directions into the loam or ancient vegetable soil on which they grew. They mark the site of a forest which existed there for a long time, since, besides the erect trunks of trees, some of them 2 and 3 feet in diameter, there is a vast accumulation of vegetable matter in the immediately overlying clays. Thirty years ago, when I first examined this bed, I saw many trees, with their roots in the old soil, laid open at the base of the cliff near Happisburgh; and long before my visit, other observers, and among them the late Mr. J.C. Taylor, had noticed the buried forest. Of late years it has been repeatedly seen at many points by Mr. Gunn, and, after the great storms of the autumn of 1861, by Mr. King. In order to expose the stumps to view, a vast body of sand and shingle must be cleared away by the force of the waves.
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 Number 3, we find a series of sands and clays with lignite (Number 3 prime), sometimes 10 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 flourished 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, north-west 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 and seeds which were collected by the Reverend S.W. King, in 1861, from the forest bed at Happisburgh, and named by Professor Heer:—
PLANTS AND SEEDS OF THE FOREST AND LIGNITE BEDS BELOW THE GLACIAL DRIFT OF THE NORFOLK CLIFFS.
- Pinus sylvestris, Scotch fir.
- Pinus abies, spruce fir.
- Taxus baccata, yew.
- Nuphar luteum, yellow water-lily.
- Ceratophyllum demersum, hornwort.
- Potamogeton, pondweed.
- Prunus spinosus, common sloe.
- Menyanthes trifoliata, buckbean.
- Nymphaea alba, white water-lily.
- Alnus, alder.
- Quercus, oak.
- Betula, birch.
The insects, so far as they are known, including several species of Donacia, 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 three elephants, a rhinoceros and hippopotamus, a large extinct beaver, and several large estuarine 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.
Those marked ٭ have been recorded by Professor Owen in his British Fossil Mammalia. Those marked † have been recognised by the same authority in the cabinets of Messrs. Gunn and King, or in the Norwich Museum; the other three are given on the authority of Dr. Falconer.
MAMMALIA OF THE FOREST AND LIGNITE BEDS BELOW THE GLACIAL DRIFT OF THE NORFOLK CLIFFS.
- Elephas meridionalis.
- ٭ Elephas primigenius.
- Elephas antiquus.
- Rhinoceros etruscus.
- ٭ Hippopotamus (major ?).
- ٭ Sus scrofa.
- ٭ Equus (fossilis ?).
- ٭ Ursus (sp.?).
- † Canis lupus.
- † Bison priscus.
- † Megaceros hibernicus.
- ٭ Cervus capreolus.
- † Cervus tarandus.
- † Cervus Sedgwickii.
- ٭ Arvicola amphibia.
- ٭ Castor (Trogontherium) Cuvieri.
- ٭ Castor europaeus.
- ٭ Palaeospalax magnus.
- † Trichecus rosmarus, Walrus.
- † Monodon monoceros, Narwhal.
- † Balaenoptera.
Mr. Gunn informs me that the vertebrae of two distinct whales were found in the fluvio-marine beds at Bacton, and that one of them, shown to Professor Owen, is said by him to imply that the animal was 60 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 prime, 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 (Figure 28), 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 Number 3, and the glacial formation 4, Figure 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 Pleistocene, or to consider them as beds of passage between the Pliocene and Pleistocene periods. The fluvio-marine series usually terminates upwards in finely laminated sands and clays without fossils, on which reposes the boulder clay.
(FIGURE 28. [omitted] Cyclas (Pisidium) amnica var.?
- The two middle figures are of the natural size.)
This formation, Number 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 6 to 8 feet in diameter have been met with, and smaller ones of syenite, 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.
(FIGURE 29. [omitted] CLIFF 50 FEET HIGH BETWEEN BACTON GAP AND MUNDESLEY.
- Section through Gravel (top), Sand, Loam and Till (bottom).)
According to the observations of the Reverend J. Gunn and the late Mr. Trimmer, the glacial drift in the cliffs at Lowestoft 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 80 feet, but it probably exceeds 100 feet near Happisburgh. 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, Number 5, Figure 27, 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 (Figure 29) represents a cliff about 50 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 5 feet thick, which, in their turn, are succeeded by vertical, bent, and contorted layers of sand and loam 20 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 their verticality to a height of 10 or 15 feet, but they have also been folded upon themselves in such a manner that continuous layers might be thrice pierced in one perpendicular boring.
(FIGURE 30. [omitted] FOLDING OF THE STRATA BETWEEN EAST AND WEST RUNTON.)
(FIGURE 31. [omitted] SECTION OF CONCENTRIC BEDS WEST OF CROMER.
- 1. Blue clay.
- 2. White sand.
- 3. Yellow Sand.
- 4. Striped loam and clay.
- 5. Laminated blue clay.)
At some points there is an apparent folding of the beds round a central nucleus, as at a, Figure 30, where the strata seem bent round a small mass of Chalk, or, as in Figure 31, where the blue clay Number 1 is in the centre; and where the other strata 2, 3, 4, 5 are coiled round it; the entire mass being 20 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 enclosure in the drift of huge fragments of Chalk many yards in diameter. One striking instance occurs west of Sheringham, where an enormous pinnacle of Chalk, between 70 and 80 feet in height, is flanked on both sides by vertical layers of loam, clay, and gravel (Figure 32).
(FIGURE 32. [omitted] INCLUDED PINNACLE OF CHALK AT OLD HYTHE POINT, WEST OF SHERINGHAM.
- d. Chalk with regular layers of flints.
- c. Layer called "the pan," of Chalk, flints, and marine shells of Recent species, cemented by oxide of iron.)
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.
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 ice-bergs 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, 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.
In the diagram of the cliffs at page 167, the bent and contorted beds Number 5, last alluded to, are represented as covered by undisturbed beds of gravel and sand Number 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 8 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 Figure 27.
(FIGURE 33. [omitted] SECTION OF THE NEWER FRESHWATER FORMATION IN THE CLIFFS AT MUNDESLEY, EIGHT MILES SOUTH-EAST OF CROMER, DRAWN UP BY THE REVEREND S.W. KING.
- Height of cliff where lowest, 35 feet above high water.
- OLDER SERIES.
- 1. Fundamental Chalk, below the beach line.
- 3. Forest bed, with elephant, rhinoceros, stag, etc., and with tree roots and stumps, also below the beach line.
- 3 prime. 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.—Number 2 of the section, Figure 27, is wanting here.
- NEWER FRESHWATER BEDS.
- A. Coarse river gravel, with shells of Anodon, Valvata, Cyclas, Succinea, Limnaea, Paludina, etc., seeds of Ceratophyllum demersum, Nuphar lutea, scales and bones of pike, perch, salmon, etc., elytra of Donacia, Copris, Harpalus, and other beetles.
- C. Yellow sands.
- D. Drift gravel.)
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 Number 3 prime 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.
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 (Figure 33) of the various beds which he has recently studied in detail.
The formations 3, 4, and 5 already described, Figure 27, were evidently once continuous, for they may be followed for miles north-west and south-east 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 prime, such as the yellow water-lily and hornwort, together with some freshwater shells which occur in the same fluvio-marine series 3 prime.
(FIGURE 34. [omitted] Paludina marginata, Michaud (P. minuta, Strickland).
- Hydrobia marginata. The middle figure is of the natural size.)
The only shell which I found not referable to a British species is the minute Paludina, Figure 34, already alluded to.
When I showed the scales and teeth of the pike, perch, roach, and salmon, which I obtained from this formation, to M. 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 before given of the freshwater deposit at Hoxne, 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, are post-glacial. It will also be seen that a long series of events, accompanied by changes in physical geography, intervened between the "forest bed," Number 3, Figure 27, when the Elephas meridionalis flourished, and the period of the Mundesley fluviatile beds A, B, C; just as in France I have shown 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, Number 3, Figure 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, Number 2, Figure 27 (the shells of which imply permanent submergence beneath the sea), and the accumulation of the uppermost of the fluvio-marine, and lignite beds, Number 3 prime, which overlie both Numbers 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 Number 4 then originated, and the gravel and sands Number 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, Number 6, Figures 27 and 33, 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 400 feet. The re-elevation must have amounted to nearly as many feet, as the site of the ancient forest, originally sub-aerial, 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, Figure 33, 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 co-existing 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, Number 4, Figures 27 and 33. The position of the Hoxne flint implements corresponds with that of the Mundesley beds, from A to D, Figure 33, 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 Number 3, or in the overlying strata 3 prime, 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 pre-glacial, would be so modern in the great geological calendar, as given in Chapter 1, that he would scarcely date so far back as the commencement of the Pleistocene period.
- In the early days of glacial geology in Britain, it was commonly accepted that the phenomena could be most satisfactorily explained on the hypothesis of a general submergence of the northern parts of the country to a depth of many hundreds of feet, and this in spite of the original comparison by Agassiz of the glacial deposits of Britain to those of the Alps. In later times, however, a school of geologists arose who attributed the glaciation of Britain to land-ice of the Continental or Greenland type. Of late years this school has been dominant in British geology, with a few notable exceptions, of whom the most important is Professor Bonney. The difficulties presented by both theories are almost equally great, and at the present time, in spite of the vehemence of the supporters of the land-ice theory, it is impossible to hold any dogmatic views on the subject. Against the doctrine of submergence is the absence of glacial deposits in places where they would naturally be expected to occur if the whole of the British Isles north of the Thames and Bristol Channel had been covered by the sea, together with the very general absence of sea-shells in the deposits. The objections to the land-ice hypothesis are largely of a mechanical nature. If we take into account the lateral extent and the thickness that can be assigned to the ice-sheet, we are at once confronted by very considerable difficulties as to the sufficiency of the driving-power behind the ice. Another great difficulty is the shallowness of the North Sea, in which a comparatively thin mass of ice would run aground at almost any point. It has been calculated that the maximum slope of the surface of the ice from Norway to the English coast could not exceed half a degree, and it is therefore difficult to see what force could compel it to move forward at all, much less to climb steep slopes in the way postulated by the extremists of this school.
- The most complete account of the geology of the Norfolk coast is contained in "The Geology of Cromer," by Clement Reid ("Memoir of the Geological Survey"). (See also Harmer, "The Pleistocene Period in the Eastern Counties of England," "Geology in the Field, the Jubilee Volume of the Geologists Association," 1909, chapter 4.). Above the Norwich Crag several more subdivisions are now recognised, and the complete succession of the Pliocene and Pleistocene strata of East Anglia may be summarised as follows:— Pleistocene:
- Peat and Alluvium
- Gravel Terraces of the present river systems
- Gravels of the old river-systems
- Plateau gravels
- Chalky boulder-clay
- Interglacial sands and gravels and Contorted Drift
- Cromer Till
- Arctic Plant Bed.
- Cromer Forest Series
- Weybourn Crag
- Chillesford Crag
- Norwich Crag
- Red Crag
- Coralline Crag.
- 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.
- "Memoirs of the Geological Survey" London 1846 page 391.
- "Quarterly Journal of the Geological Society" volume 5 1849 page 345.
- It is now generally agreed that the tree-stumps in the Cromer Forest bed are not in the position of growth. Many of them are upside down or lying on their sides, and they were probably floated into their present position by the waters of a river flowing to the north. This river was a tributary of the Rhine which then flowed for several hundred miles over a plain now forming the bed of the North Sea, collecting all the drainage of eastern England, and debouching into the North Atlantic somewhere to the south of the Faroe Isles. (See Harmer, "The Pleistocene Period in the Eastern Counties of England," "Geological Association Jubilee Volume," London, 1909, pages 103 to 123.)
- Mr. King discovered in 1863, in the forest bed, several rhizomes of the large British fern Osmunda regalis, of such dimensions as they are known to attain in marshy places. They are distinguishable from those of other British ferns by the peculiar arrangement of the vessels, as seen under the microscope in a cross section.
- Of late years an enormous number of characteristic rocks from Norway and Sweden have been recognised in the drifts of Eastern England, as far south as Essex and Middlesex. One of the most easily identifiable types is the well-known Rhombporphyry of the Christiania Fjord, a rock which occurs nowhere else in the world, and is quite unmistakable in appearance. Along with it are many of the distinctive soda-syenites found in the same district, the granites of southern Sweden, and many others. The literature of the subject is very large, but many details may be found in the annual reports of the British Association for the last twenty years. From a study of these erratics it has been found possible to draw important conclusions as to the direction and sequence of the ice streams which flowed over these regions during the different stages of the glacial period.
- "Quarterly Journal of the Geological Society" volume 7 1851 page 21.
- For a full account of the drift of East Norfolk, see a paper by the author, "Philosophical Magazine" Number 104 May 1840.
- "Quarterly Journal of the Geological Society" volume 7 1851 pages 22, 30.
- See "Manual of Geology" by the author, page 51.
- "Philosophical Magazine" volume 16 1840 page 345.
- Mr. Prestwich has given a correct account of this section in a paper read to the British Association, Oxford, 1860. See "The Geologist" volume 4 1861.
- This shell is said to have a sub-spiral operculum (not a concentric one, as in Paludina), and therefore to be referable to the Hydrobia, a sub-genus of Rissoa. But this species is always associated with freshwater shells, while the Rissoae frequent marine and brackish waters.