Popular Science Monthly/Volume 12/November 1877/Man and the Glacial Period
|MAN AND THE GLACIAL PERIOD.|
CONCERNING the Glacial period, geologists hold the most varied opinions, both with regard to its origin and to the mode of action of the ice. Thus at the very threshold of the geological record we tread on uncertain ground, and every guide points to a different path. The relation that palæolithic man bore to the great ice age might seem to be of easier solution; but even this question is unsettled, and a subject of controversy and doubt. Prof. Prestwich is believed by many to have proved that palæolithic man was postglacial. Messrs. Croll and Geikie urge that there were two or more glacial periods in post-tertiary times, and that he nourished in a mild interglacial period. I, on the contrary, have been gradually forced to conclude that, in the British Isles, all the remains in caves and valley-gravels referred to palæolithic man are preglacial, in the sense that they are of earlier date than the glaciation of the districts in which they are found.
I propose to state briefly some of the general arguments that have influenced my opinion, and then to deal with the special question of the age of the deposits at Hoxne, which the advocates of the postglacial theory put forward as being undoubtedly in their favor.
Let us first take into consideration the age of the beds containing the remains of the mammoth, the woolly rhinoceros, and their companions, with which the palæolithic implements are so often found. Wherever, in Europe, the relation of these beds to the bowlder-clay can be clearly seen, they are of distinctly older age. Thus, in Russia, Sir Roderick I. Murchison has recorded the discovery of the bones of the mammoth and woolly rhinoceros, near Moscow, in reddish clay covered with erratic blocks, on the plains thirteen miles distant from the river. And if we follow the northern drift southward from Moscow, as I have done, we find it gradually changes from clay with bowlders to the clay without bowlders that covers the southern plains. Around the sea of Azov, cliffs of this glacial clay, one hundred feet high, can be followed continuously for miles, and its junction below with the older beds is sharply defined. It rests on a fresh-water deposit containing shells of species of Unto, Cyclas, and Paludina, and at this horizon fragments of the tusks and bones of the mammoth are abundant, and are always undoubtedly older than the glacial clay. In a similar position the same remains have been found at Odessa and other places in the south of Russia.
Nor has the theory of the post-glacial age of the remains of the mammoth remained unchallenged by eminent geologists in England. Prof. Phillips and Mr. Godwin Austen long ago recorded their conviction that they belonged to an earlier period than the deposition of the bowlder-clay, and that when they occur in newer beds they have been derived from an older formation. The remains are so plentiful in the caves of the north of England that it is certain that the mammoth and rhinoceros were abundant. Yet nowhere in the glaciated parts of the country have the bones been found excepting where preserved from the action of the ice in caverns and fissures.
Thus, in tracing the limits of the northern ice on the eastern side of England, I have found that Durham and Northumberland were probably completely overflowed by it, excepting the upper parts of the Cheviots, as pointed out to me by Mr. Richard Howse. The ice streamed through from the west, around the southern and northern flanks of the Cheviots, down the valleys of the Tyne and the Tweed, and when approaching the eastern coast was deflected to the south by the great mass of ice that occupied and was flowing down the bed of the German Ocean. In Yorkshire the ice from the west was held back by the Pennine Chain, and did not coalesce with the German Ocean glacier, but stopped short, somewhere about an irregular line drawn from Keighley, northeastward to near the mouth of the Tees. The German Ocean glacier only, as it were, grazed the high land bordering the coast until it reached the northern shores of Norfolk that stood out across its track. A large portion of Yorkshire was thus never glaciated by land-ice, and in this area remains of the great extinct mammals have been found in and below the lowland gravels, as at Leeds and Market Weighton; but when we pass northwestward into the country where the striæ on the rock-surfaces bear witness to the passage of land-ice, no such remains are found, excepting in caverns and fissures of the old rocks.
The northwestern side of England is much more glaciated than the northeastern, and the mammalian remains have only been found where preserved in caves. The ice filling the Irish Sea reached to a height of 2,000 feet on the western flank of the Pennine Chain. Probably reënforced from the westward it continued, in scarcely decreasing thickness, across the whole of Lancashire and Cheshire, and passed over into the drainage area of the Severn, down which valley it appears to have flowed for some distance. As soon as we get beyond its influence we again meet with mammalian remains in the lowland gravels, and in most of the southern valleys they are abundant.
If the mammoth and its associates roamed as far as the north of England, and even into Scotland, after the Glacial period, their remains ought to be found in the valley-gravels of the glaciated districts. They are, however, absent; and if we should be led to infer from this that they lived before the glaciation of the country, and accept the conclusion of Prof. Phillips and Mr. Godwin Austen that the mammoth and the woolly rhinoceros lived before and not after the Glacial period in Great Britain, we can scarcely refrain from going further than these geologists and concluding that the makers of the palæolithic implements were also preglacial. For no geological inference seems based upon sounder evidence than that palæolithic man was contemporaneous with the mammoth and its associates. The implements of the one and the bones of the others are found together in the same stratum of the cave-earth, and in all the numerous caverns that have been searched in England and Wales there is no record of palæolithic implements being found at a higher horizon; when flint weapons do so occur they are invariably of the neolithic type. If geological evidence of contemporaneity is of any value, the occupation of the caves by palæolithic man ceased at the same time as the great mammals disappeared.
Let us look at the question from another point of view. In the south of England the remains of the mammoth are abundant in the valley-gravels. They are found mixed through them, or more commonly at their base. Palæolithic implements are found in the same position, though usually in gravel higher up on the slopes of the valleys. When found in the gravel, the bones are broken and worn, and the flint implements have their angles rounded more or less as if by rolling. When, as has happened in a few cases, the bones and implements have been found below the gravels, they have been uninjured and unworn. Mr. Godwin Austen noticed the occurrence of bones of the mammoth in an old forest-bed beneath the valley-gravels, at Pease marsh, in Surrey, uninjured and lying together, while in the overlying gravel the teeth of the mammoth were found singly and rolled. And Colonel Lane Fox has recorded the discovery of flint implements at Acton in seams of white sand, nine feet from the surface, beneath deposits of gravel and brick-earth. Their edges were as sharp as if just flaked off a core of flint; while those found in the gravel, on the contrary, have their edges worn and rounded just like those of the subangular pebbles of which the gravel is principally composed.
The position and the state of preservation of the bones and implements are such as might be expected if they had been deposited on an old land-surface before the outspread of the gravels, when the configuration of the country was much the same as now; and I have suggested that the occurrence of the implements, generally higher up the slopes of the valleys than the mammalian remains, is due to palæolithic man having frequented more elevated and drier localities than the great mammals. I have urged that the outspread of the gravels was due, as formerly supposed by Sedgewick, De la Beche, and Murchison, to the action of a great flood or debacle. I have advanced the theory that that debacle was caused by the breaking away of a barrier of ice that blocked up the English Channel, and with it nil the drainage of Northern Europe, causing an immense lake of fresh or brackish water that was thus suddenly and tumultuously discharged.
This great flood occurred, according to my theory, before the culmination of the Glacial period, and was primarily due to ice filling the bed of the North Atlantic as far south on the European side as latitude 49°. If the gravels in and below which the rude flint implements and the remains of the extinct mammals are found, were thus spread out, it follows that they were preglacial in the sense that they lived before the principal glaciation of the country.
We have seen that, in the north, such an excellent geologist as the late Prof. Phillips had arrived at this conclusion with regard to the age of the mammoth, the woolly rhinoceros, and the hippopotamus; and, in the south, Mr. Godwin Austen, from a study of the same remains in the valley-gravels. Direct evidence of great value has been added by Mr. Tiddiman in his reports on the exploration of the Victoria Cave, at Settle. He has shown that the cave-deposits lie beneath glacial clay, and, among the other remains, a human fibula has been found. In the Cefn Cave, in Denbighshire, Mr. Mackintosh has also determined that the mammalian remains lie in and below a glacial clay.
All the lines of inquiry thus far pursued in this paper point to the preglacial age of the remains in question, and some of the facts are directly opposed to the post-glacial theory. How, then, is it that the great majority of geologists write as if it had been clearly proved that palæolithic man was of post-glacial age? Principally because it is believed that Prof. Prestwich has proved that at Hoxne, in Suffolk, the implements and bones are found in deposits distinctly overlying bowlder-clay. This is spoken of as if it were a truism in most general treatises on geology; and both in Europe and America the presumption is appealed to as being conclusive with regard to the age of the remains. The general opinion held is concisely given in the statement by Mr. John Evans in his presidential address to the Geological Society last year, that, at Hoxne, "the implement-bearing beds repose in a trough cut out in the upper glacial bowlder-clay, which itself rests on middle glacial sands and gravels."
This opinion of the age of the Hoxne deposits is founded on the elaborate memoir by Prof. Prestwich, published in the "Philosophical Transactions of the Royal Society," for 1860. In this treatise the author gives a diagram showing the deposits in question lying in a trough cut out in the bowlder-clay. Though this section is confessedly only theoretical, it was accepted by Sir Charles Lyell and others as an actual one, and afterward the author himself wrote as if he had proved his theory to be true, which he may well be excused for having done, when it had been accepted by so many eminent geologists.
The writings of Prof. Prestwich are admirable in this, as in other respects, that, although he indulges in wide-reaching theories, he invariably gives the evidence on which they are founded. Thus, in the memoir in question, in addition to the theoretical diagram he gives another, showing the actual facts observed, and also careful details of the various sections observed by him. It is, therefore, possible to check his theory by his facts, and in the present paper I shall do so, and also give the results of my own examination of the Hoxne district.
Mr. John Frere, so long ago as the first year of the present century, communicated to the Society of Antiquaries an "Account of Flint Weapons discovered at Hoxne, in Suffolk." He stated that they were found in great numbers in a bed of gravel, which was overlaid by one foot of sand with shells, and containing the jawbone and teeth of an enormous animal; the sand being again covered by seven and a half feet of brick-clay. Mr. Frere noticed that the strata lay horizontally, and had been denuded to form the present valley, and therefore concluded that they belonged to a period when the configuration of the surface was different from what it is now, and he considered that their antiquity was possibly "even beyond that of the present world." The manner in which the flint implements lay, and their great abundance, led Mr. Frere to conclude that a manufactory of them had been carried on at the place where he found them.
The discovery does not appear to have excited any attention at the time, and for more than half a century remained unnoticed. In 1859, when the discovery of flint implements in the valley of the Somme, in France, in association with the remains of the mammoth and other extinct mammals, had at last aroused the attention of geologists, Mr. Frere's memoir was brought by Mr. John Evans before the notice of Mr. Prestwich, who had just returned from Amiens. He soon after visited Hoxne, and carefully examined into the facts of the case. He found that the bed of brick-clay was still being worked, and that flint implements were occasionally, though rarely, turned up; and on a subsequent visit with Mr. Evans they succeeded in disinterring one themselves.
The valleys of the Waveney and its tributaries are bounded by low hills of gravel and bowlder-clay. The bed-rock is not seen in any of the sections exposed, but it is supposed to be chalk. The gravels and sands (the middle glacial sands and gravels of Mr. Searles Wood, Jr.) are exposed in many gravel-pits on both sides of the Waveney. They are sometimes capped by the upper bowlder-clay; at others, by a more sandy bed with stones (the "trail" of Mr. Fisher), which in some of the sections graduates into the upper bowlder-clay, of which I believe it to be the modified representative. One of the deepest sections on the north bank of the Waveney is near the road from Diss to Harleston, at Billingford, where the series of beds shown in Fig. 1 are exposed.
Mr. Fisher some time ago called attention to the great importance of the upper bed, or "trail," in the study of the glacial beds, but it has not yet received the notice it deserves. It is the most persistent of all the beds in the southeastern counties, and can be traced, in almost every section, from Norfolk into Surrey. It is everywhere seen in the Thames Valley lying on the top of the lowland gravels, and is shown in great perfection in the long section now (March, 1876) exposed between Acton and Hanwell, on the Great Western Railway.
It generally, if not always, rests upon an irregular surface of the beds below it, and contains stones derived from some other source.
On the south side of the Waveney, at Syleham, there are good sections on both sides of the turnpike, and these exhibit similar false-bedded sands and gravels, which are, however, covered by the upper bowlder-clay instead of by "trail." Fig. 2 shows a section exposed
on the south side of the turnpike. A little farther west, on the north side of the turnpike, is another gravel-pit, showing a similar succession, but with the beds of sand and gravel strongly false-bedded. In all these sections small pebbles of chalk are very abundant in the lowest beds. The most remarkable feature in the upper bowlder-clay is the numerous angular patches of material quite different from the matrix of brown clay. The angular patches of red sand are very peculiar and difficult to explain.
In a large gravel-pit a little north of Oakley Church there is a long section exposed, and in it the upper bowlder-clay, similar to that shown in Fig. 2, at one end of the pit, gradually changes into a sandy loam with stones and angular patches of sand, not to be distinguished from the deposit named "trail" in Fig. 1.
At Hoxne itself, on the east side of Gold Brook, there is a gravel-pit showing seams of gravel and sand exactly similar to that at Syleham, but surmounted by sandy "trail" instead of by bowlder-clay. The gravel is not to be distinguished from the other, being composed like it of subangular flint-pebbles with rounded ones of quartz and quartzite, and with many small pebbles of chalk in the lowest seams. Notwithstanding this great similarity, Mr. Prestwich considers the beds at Hoxne to have been formed by river-action in post-glacial times; while those at Syleham, being capped by bowlder-clay, he of necessity classifies as middle glacial. Yet I could find no difference whatever in their appearance or composition. In both the pebbles are mostly small and subangular, with some rounded ones of quartz and quartzite. Both contain many small pebbles of chalk in their lowest seams, and both are false-bedded. That one is covered with bowlder-clay and the other by sandy "trail" does not suffice to prove them of different age, for at the Oakley gravel-pit we can trace the same gravels from one end, where the bowlder-clay overlies them, to the other, where the "trail" does so. The middle sands and gravels are generally supposed by geologists to be marine, and it is incredible that deposits due to such different agencies as that of the waves of the ocean beating on a beach and that of a flooded river should be absolutely identical in appearance and composition. But nowhere is either the ocean or any river known to be forming deposits of subangular pebbles, excepting where they are cutting into preexisting beds of the middle glacial series. Both in sea and in river beaches the pebbles are smoothly rounded, and not, as in the gravels under consideration, broken and subangular. Even when we find in the latter rounded pebbles of tertiary age there is often a piece chipped out of them as if they had been dashed violently together. I have had a large number of the pebbles from the gravel at Ealing counted, and find that over eighty per cent, are broken or subangular. I ask where, in the whole world, is such a deposit being formed by existing agencies? Surely, if ordinary floods would produce them, they have had plenty of opportunities of doing so during the past pluvial year; yet where, on the banks of any of our rivers, have the great floods left deposits even approaching in character to those that geologists confidently ascribe to river-action? That they were caused by a great flood I fully believe, though not by that of any river, but by one that swept over the whole country, driving a huge mass of gravel and sand, and leaving them mantling both hills and valleys, holding or covering up the remains of palæolithic man and the great mammals that had lived before the waters were pent up by the Atlantic glacier.
A little above Hoxne, on the left side of the stream called the Gold Brook, is the Hoxne clay-pit. The clay is excavated along the slope of the shallow valley through which the brook runs. The road to Eye skirts the hill-side, having to the west the park of Sir Edward Kerrison; and to the east, between it and the stream, a narrow strip
of land from which the clay has been dug. The old workers had commenced near the village of Hoxne, and as they gradually exhausted the clay up to the road they moved farther southward, and the point at which it is now excavated is probably at least a quarter of a mile distant from that where Mr. Frere made his discoveries in 1800. The pit has now been worked up to some farm-buildings that interfere with its progress southward, and to get clay they have now crossed the road into the park, and thus made a most important addition to the section laid open.
I have in the accompanying plate given three sections of the ground. The first shows the theoretical relation of the beds according to Prof. Prestwich; the second exhibits the facts actually observed by Prof. Prestwich and myself; and the third is a theoretical section showing the relation that the beds hold to each other according to my own views. We shall in the first place confine our attention to the second section (Fig. 4), showing the facts actually observed.
On the east side of Gold Brook a cutting has been made into the bank, and a thick bed of bowlder-clay is exposed. At the point A in general section the beds are shown, as in Fig. 6. Near the line of division the upper and more chalky clay contains many large flints and transported bowlders. Some of these are smoothed, and strongly scratched and grooved. Two scratched blocks of septaria that I saw measured one and a half foot across. This bowlder-clay, both in its upper and lower division, is very distinct in appearance and composition from that lying above the gravels, as seen in other sections. Lower down toward the brook a seam of false-bedded sandy gravel comes in between the bowlder-clay and the "trail," and represents, I think, the gravels of Figs. 1 and 2.
Crossing the brook and ascending the opposite slope, we have, at the points C and D of general section, typical sections of the clay, pit, as shown in Fig. 7. The clay (4 in section) is called "red-brick earth" by the workmen, because it burns to a red color; while the lower, dark-colored clay (7 in section) is called "white-brick earth," because it burns to a white color. The bottom of the latter bed has not been reached, although Prof. Prestwich had a boring put down into it to a depth of seventeen feet. It is full of vegetable matter, and I found numerous pieces of wood in it. The men pointed out to me the gravel-seams (5 in section), as the horizon at which flint implements had been found; but, shortly before Prof. Prestwich visited the pit, two specimens had been taken from the lower part of the clay (4 in section). There can be little doubt, however, that they were found by Mr. Frere in the gravel below the "red-brick earth," as he says that "they lay in great numbers at the depth of about twelve feet in
a stratified soil, which was dug into for the purpose of raising clay for bricks. Under a foot and a half of vegetable earth was clay seven and a half feet thick, and beneath this one foot of sand with shells, and under this two feet of gravel, in which the shaped flints were found generally at the rate of five or six in a square yard. The manner in which the flint implements lay would lead to the persuasion that it was a place of their manufacture, and not of their accidental deposit. Their numbers were so great that the man who carried on the brickwork told me that, before he was aware of their being objects of curiosity, he had emptied baskets full of them into the ruts of the adjoining road."
As I have already mentioned, the place at which the clay is now excavated is some distance from that where Mr. Frere found the implements, and they are now very seldom met with—so seldom, that none of the men working at the clay-pit when I was there had ever seen one.
To the west of the road, in the pit that has been opened in Sir Edward Kerrison's park, a section of the beds has been exposed at the point marked E in general section, as shown in Fig. 8. The most remarkable feature in the section is the occurrence of the upper clay (2 in section), containing angular patches of red sand, like that seen in the "upper bowlder-clay" of other parts of the district. I cannot help thinking that, if this section had been open when Prof. Prestwich examined the deposits, he would have been led to modify his opinion respecting the relation of the deposits to the Glacial period. I myself believe this clay to be the upper bowlder-clay, and the sand with pebbles below it to be the "middle glacial sands and gravels."
To trace the "red-brick earth" (4 in section) down toward the lower bowlder-clay, I set some men to work, and had a shaft sunk—at the point marked B in general section—to a depth of seventeen feet from the top of the surface-soil, and obtained the section shown in Fig. 9. The most noticeable feature in this section is the thickening out of the false-bedded sands and gravels, their resemblance to the middle glacial series, and the absence of the "white-brick earth" (7 in section). In a pit a little east of this, Prof. Prestwich and Mr. John Evans found a flint implement in the gravel-bed (3 in section).
I have now given all the facts at present known respecting the relation of these beds to the Glacial period, and I proceed to the consideration of Prof. Prestwich's theoretical views, as shown in the general section (Fig. 3). In the first place, Prof. Prestwich identifies the bowlder-clay seen in the pit on the east side of the brook as the upper bowlder-clay. As I have already mentioned, it in no respect resembles the clay seen in other sections above the false-bedded sands and gravel, and the existence of the middle glacial beds below this particular deposit is entirely theoretical. Prof. Prestwich makes these sands and gravel to pass under the brick-clays; and I feel confident it will astonish many of those who appeal to this section, as proof of the post-glacial age of palæolithic man, to learn that they have never been seen in this position, and that their presence is an assumption only. The "red-brick earth" ought, according to Prof. Prestwich's views, to thin out eastward, and the dark clays or "red-brick earth" to crop up to the surface from underneath it. Instead of this, as shown in Fig. 8, at the point B in general section, the "red-brick earth" follows down the slope of the hill, and is not underlaid at all at that point by the dark clays. I do not, however, attach much importance to this, as the "red-brick earth" might mantle the hill, overlapping the edge of the dark clays, and yet Prof. Prestwich's general idea of the relation of the latter to the glacial beds be correct. What I do wish to point out is, that that relation is not proved by any of the facts known, and that an entirely different interpretation is not only possible, but more probable. That other interpretation I have indicated in the general section (Fig. 5), in which all the facts observed are incorporated. I consider that the dark clay with vegetable remains and bones of the large extinct mammals is preglacial, in the sense that it is older than any of the glacial beds of the district. The gravel below the "redbrick earth," in which Mr. Frere found the flint implements, is probably of the same age, or that of the overlying gravel (5 in Figs. 4 and 5). That the implements, and also fragments of bones and wood, should be occasionally found in the overlying deposits, is what might be expected, as they were in great measure formed by the denudation of the older ones. The " red-brick earth " (4 in section) is, I believe, a true glacial clay, belonging to the latter part of the first European lake. It is a noticeable fact that, all over Northern Europe, the glacial clays burn to a red color—a point not without significance with regard to the red beds of Permian
or Triassic age. The false-bedded sands and gravels (3 in Figs. 4 and 5) belong, I think, to the middle glacial series, and the clay (2 in Figs. 4 and 5) is, I think, the upper bowlder-clay. These views are only theoretical, but I claim that they are based upon as sound a foundation, and are as much in accordance with the facts of the case, as those generally received.
Another interpretation is tenable, namely, that the lower bowlder-clay underlies the brick-clays, and that the upper bowlder-clay overlies them, while they themselves belong to a warm interglacial period, as held by Messrs. Croll and Geikie. I do not agree with this opinion, as I can nowhere find any evidence of a warm interglacial period, and am unwilling: to believe that there were more post-tertiary glacial periods than one, when one will explain all the phenomena; but if it were to turn out that the lower bowlder-clay does exist beneath the brick-clays at Hoxne, it would be one of the strongest facts in its favor yet brought forward.
I now come to the real point and object of this paper. We have in England, at Hoxne, one of the finest opportunities known to exist anywhere in Europe of determining the true relation that the beds containing remains of palæolithic man and the great extinct Mammalia bear to the Glacial period; yet we have been content for more than a dozen years to allow the age of the beds that underlie these deposits to remain a conjecture, and to accept a theory instead of ascertaining what are the true facts of the case. The geological world has been taught to believe that a question was settled that is not settled. We do know the age of the Hoxne deposits: they may, as held by Prof. Prestwich, be postglacial; or they may, as held by Messrs. Croll and Geikie, be interglacial; or, lastly, they may, as I hold, be preglacial.
It is not creditable that this uncertainty should remain when it can easily be cleared up. A few shafts or bore-holes put down would soon determine whether or not glacial beds underlie the dark clays of the brick-pit, or sands and gravel underlie the bowlder-clay on the other side of the brook. Excavations should also be made around the spot where Mr. Frere made his discoveries, to ascertain the exact position in which the flint implements were found so abundantly. I feel satisfied that, if Sir Edward Kerrison, to whom the property belongs, were applied to by any of our learned societies, he would willingly allow the necessary excavations to be made. Probably the expenditure of two hundred pounds would be amply sufficient, and I submit that it is a work that should be undertaken by the Royal Society or the British Association, who make grants for scientific inquiry.—Quarterly Journal of Science.
- "Geology of Russia in Europe," p. 650.
- "Geology of Yorkshire," 1829, vol. i., pp. 18, 52.
- "British Association Reports," 1863, p. 68.
- Quarterly Journal of the Geological Society, vol. vii., p. 288.
- Ibid., vol. xxviii., p. 456.
- Quarterly Journal of Science, April, 1875. Quarterly Journal of the Geological Society, vol. xxxii., p. 84.
- Nature, vol. ix., p. 14. "British Association Reports," for 1873, 1874, 1875.
- Quarterly Journal of the Geological Society, vol. xxxii., p. 91.
- Sir Charles Lyell, "Antiquity of Man," p. 166. J. Geikie, "Great Ice Age," p. 474. J. Croll, "Climate and Time," p. 241. W. Boyd Dawkins, "Cave-Hunting," p. 410. Jukes's "Students' Manual of Geology," p. 736.
- Quarterly Journal of the Geological Society, vol. xxxi., p. 74.
- "Philosophical Transactions," 1864, p. 253.
- "Archæologia," 1800, vol. xiii., p. 206.
- Quarterly Journal of the Geological Society, vol. xxii., p. 553.