Penultimate molar, lower jaw, right side, one-third of natural size, Newer Pliocene, Saint Prest, near Chartres, and Norwich Crag. Not yet proved to have coexisted with Man.)

(* For Figure 20 I am indebted to M. Lartet, and Figure 18 will be found in his paper in "Bulletin de la Societe Geologique de France" March 1859. Figure 19 is from Falconer and Cautley "Fauna Sivalensis.")

Immediately below Amiens, a great ma.s.s of stratified gravel, slightly elevated above the alluvial plain of the Somme, is seen at St. Roch, and half a mile farther down the valley at Montiers. Between these two places a small tributary stream, called the Celle, joins the Somme. In the gravel at Montiers, Mr. Prestwich and I found some flint knives, one of them flat on one side, but the other carefully worked, and exhibiting many fractures, clearly produced by blows skilfully applied. Some of these knives were taken from so low a level as to satisfy us that this great bed of gravel at Montiers, as well as that of the contiguous quarries of St. Roch, which seems to be a continuation of the same deposit, may be referred to the human period. Dr. Rigollot had already mentioned flint hatchets as obtained by him from St. Roch, but as none have been found there of late years, his statement was thought to require confirmation. The discovery, therefore, of these flint knives in gravel of the same age was interesting, especially as many tusks of a hippopotamus have been obtained from the gravel of St. Roch--some of these recently by Mr. Prestwich; while M. Garnier of Amiens has procured a fine elephant's molar from the same pits, which Dr. Falconer refers to Elephas antiquus, see Figure 19. Hence I infer that both these animals co-existed with Man.

The alluvial formations of Montiers are very instructive in another point of view. If, leaving the lower gravel of that place, which is topped with loam or brick-earth (of which the upper portion is about 30 feet above the level of the Somme), we ascend the Chalk slope to the height of about 80 feet, another deposit of gravel and sand, with fluviatile sh.e.l.ls in a perfect condition, occurs, indicating most clearly an ancient river-bed, the waters of which ran habitually at that higher level before the valley had been scooped out to its present depth. This superior deposit is on the same side of the Somme, and about as high, as the lowest part of the celebrated formation of St. Acheul, 2 or 3 miles distant, to which I shall now allude.

The terrace of St. Acheul may be described as a gently sloping ledge of Chalk, covered with gravel, topped as usual with loam or fine sediment, the surface of the loam being 100 feet above the Somme, and about 150 above the sea.

Many stone coffins of the Gallo-Roman period have been dug out of the upper portion of this alluvial ma.s.s. The trenches made for burying them sometimes penetrate to the depth of 8 or 9 feet from the surface, entering the upper part of Number 3 of the sections Figures 21 and 22.

They prove that when the Romans were in Gaul they found this terrace in the same condition as it is now, or rather as it was before the removal of so much gravel, sand, clay, and loam, for repairing roads, and for making bricks and pottery.

[Ill.u.s.tration: Figure 21. Section of Gravel Pit]

(FIGURE 21. SECTION OF GRAVEL PIT CONTAINING FLINT IMPLEMENTS AT ST. ACHEUL, NEAR AMIENS, OBSERVED IN JULY 1860.

1. Vegetable soil and made ground, 2 to 3 feet thick.

2. Brown loam with some angular flints, in parts pa.s.sing into ochreous gravel, filling up indentations on the surface of Number 3, 3 feet thick.

3. White siliceous sand with layers of chalky marl, and included fragments of Chalk, for the most part unstratified, 9 feet.

4. Flint-gravel, and whitish chalky sand, flints subangular, average size of fragments, 3 inches diameter, but with some large unbroken Chalk flints intermixed, cross stratification in parts. Bones of mammalia, grinder of elephant at b, and flint implement at c, 10 to 14 feet.

5. Chalk with flints.

a. Part of elephant's molar, 11 feet from the surface.

b. Entire molar of Elephas primigenius, 17 feet from the surface.

c. Position of flint hatchet, 18 feet from the surface.)

In the annexed section (Figure 21), which I observed during my last visit in 1860, it will be seen that a fragment of an elephant's tooth is noticed as having been dug out of unstratified sandy loam at the point a, 11 feet from the surface. This was found at the time of my visit; and at a lower point, at b, 18 feet from the surface, a large nearly entire and unrolled molar of the same species was obtained, which is now in my possession. It has been p.r.o.nounced by Dr. Falconer to belong to Elephas primigenius.

A stone hatchet of an oval form, like that represented at Figure 9, was discovered at the same time, about one foot lower down, at c, in densely compressed gravel. The surface of the fundamental Chalk is uneven in this pit, and slopes towards the valley-plain of the Somme. In a horizontal distance of 20 feet, I found a difference in vertical height of 7 feet. In the chalky sand, sometimes occurring in interstices between the separate fragments of flint, const.i.tuting the coa.r.s.e gravel Number 4, entire as well as broken freshwater sh.e.l.ls are often met with.

To some it may appear enigmatical how such fragile objects could have escaped annihilation in a river-bed, when flint tools and much gravel were shoved along the bottom; but I have seen the dredging instrument employed in the Thames, above and below London Bridge, to deepen the river, and worked by steam power, scoop up gravel and sand from the bottom, and then pour the contents pell-mell into the boat, and still many specimens of Limnaea, Planorbis, Paludina, Cyclas, and other sh.e.l.ls might be taken out uninjured from the gravel.

It will be observed that the gravel Number 4 is obliquely stratified, and that its surface had undergone denudation before the white sandy loam Number 3 was superimposed. The materials of the gravel at d must have been cemented or frozen together into a somewhat coherent ma.s.s to allow the projecting ridge, d, to stand up 5 feet above the general surface, the sides being in some places perpendicular. In Number 3 we probably behold an example of a pa.s.sage from river-silt to inundation mud. In some parts of it, land sh.e.l.ls occur.

It has been ascertained by MM. Buteux, Ravin, and other observers conversant with the geology of this part of France, that in none of the alluvial deposits, ancient or modern, are there any fragments of rocks foreign to the basin of the Somme--no erratics which could only be explained by supposing them to have been brought by ice, during a general submergence of the country, from some other hydrographical basin.

But in some of the pits at St. Acheul there are seen in the beds Number 4, Figure 21, not only well-rounded Tertiary pebbles, but great blocks of hard sandstone, of the kind called in the south of England "greywethers," some of which are 3 or 4 feet and upwards in diameter.

They are usually angular, and when spherical owe their shape generally to an original concretionary structure, and not to trituration in a river's bed. These large fragments of stone abound both in the higher and lower level gravels round Amiens and at the higher level at Abbeville. They have also been traced far up the valley above Amiens, wherever patches of the old alluvium occur. They have all been derived from the Tertiary strata which once covered the Chalk. Their dimensions are such that it is impossible to imagine a river like the present Somme, flowing through a flat country, with a gentle fall towards the sea, to have carried them for miles down its channel unless ice co-operated as a transporting power. Their angularity also favours the supposition of their having been floated by ice, or rendered so buoyant by it as to have escaped much of the wear and tear which blocks propelled along the bottom of a river channel would otherwise suffer.

We must remember that the present mildness of the winters in Picardy and the northwest of Europe generally is exceptional in the northern hemisphere, and that large fragments of granite, sandstone, and limestone are now carried annually by ice down the Canadian rivers in lat.i.tudes farther south than Paris.*

(* "Principles of Geology" 9th edition page 220.)

[Ill.u.s.tration: Figure 22. Contorted Strata]

(FIGURE 22. CONTORTED FLUVIATILE STRATA AT ST. ACHEUL (Prestwich, "Philosophical Transactions" 1861, page 299).

1. Surface soil.

2. Brown loam as in Figure 21, thickness, 6 feet.

3. White sand with bent and folded layers of marl, thickness, 6 feet.

4. Gravel, as in Figure 21, with bones of mammalia and flint implements.

A. Graves filled with made ground and human bones.

b and c. Seams of laminated marl often bent round upon themselves.

d. Beds of gravel with sharp curves.)

Another sign of ice agency, of which Mr. Prestwich has given a good ill.u.s.tration in one of his published sections, and which I myself observed in several pits at St. Acheul, deserves notice. It consists in flexures and contortions of the strata of sand, marl, and gravel (as seen at b, c, and d, Figure 22), which they have evidently undergone since their original deposition, and from which both the underlying Chalk and part of the overlying beds of sand Number 3 are usually exempt.

In my former writings I have attributed this kind of derangement to two causes; first, the pressure of ice running aground on yielding banks of mud and sand; and, secondly, the melting of ma.s.ses of ice and snow of unequal thickness, on which horizontal layers of mud, sand, and other fine and coa.r.s.e materials had acc.u.mulated. The late Mr. Trimmer first pointed out in what manner the unequal failure of support caused by the liquefaction of underlying or intercalated snow and ice might give rise to such complicated foldings.*

(* See chapter 12.)

When "ice-jams" occur on the St. Lawrence and other Canadian rivers (lat.i.tude 46 degrees north), the sheets of ice, which become packed or forced under or over one another, a.s.sume in most cases a highly inclined and sometimes even a vertical position. They are often observed to be coated on one side with mud, sand, or gravel frozen on to them, derived from shallows in the river on which they rested when congelation first reached the bottom.

As often as portions of these packs melt near the margin of the river, the layers of mud, sand, and gravel, which result from their liquefaction, cannot fail to a.s.sume a very abnormal arrangement--very perplexing to a geologist who should undertake to interpret them without having the ice-clue in his mind.

Mr. Prestwich has suggested that ground-ice may have had its influence in modifying the ancient alluvium of the Somme.*

(* Prestwich, Memoir read to Royal Society, April 1862.)

It is certain that ice in this form plays an active part every winter in giving motion to stones and gravel in the beds of rivers in European Russia and Siberia. It appears that when in those countries the streams are reduced nearly to the freezing point, congelation begins frequently at the bottom; the reason being, according to Arago, that the current is slowest there, and the gravel and large stones, having parted with much of their heat by radiation, acquire a temperature below the average of the main body of the river. It is, therefore, when the water is clear, and the sky free from clouds, that ground ice forms most readily, and oftener on pebbly than on muddy bottoms. Fragments of such ice, rising occasionally to the surface, bring up with them gravel, and even large stones.

Without dwelling longer on the various ways in which ice may affect the forms of stratification in drift, so as to cause bendings and foldings in which the underlying or over-lying strata do not partic.i.p.ate, a subject to which I shall have occasion again to allude in the sequel, I will state in this place that such contortions, whether explicable or not, are very characteristic of glacial formations. They have also no necessary connection with the transportation of large blocks of stone, and they therefore afford, as Mr. Prestwich remarks, independent proof of ice-action in the Pleistocene gravel of the Somme.

Let us, then, suppose that, at the time when flint hatchets were embedded in great numbers in the ancient gravel which now forms the terrace of St. Acheul, the main river and its tributaries were annually frozen over for several months in winter. In that case, the primitive people may, as Mr. Prestwich hints, have resembled in their mode of life those American Indians who now inhabit the country between Hudson's Bay and the Polar Sea. The habits of those Indians have been well described by Hearne, who spent some years among them. As often as deer and other game become scarce on the land, they betake themselves to fishing in the rivers; and for this purpose, and also to obtain water for drinking, they are in the constant practice of cutting round holes in the ice, a foot or more in diameter, through which they throw baited hooks or nets.

Often they pitch their tent on the ice, and then cut such holes through it, using ice-chisels of metal when they can get copper or iron, but when not, employing tools of flint or hornstone.

The great acc.u.mulation of gravel at St. Acheul has taken place in part of the valley where the tributary streams, the Noye and the Arve, now join the Somme. These tributaries, as well as the main river, must have been running at the height first of 100 feet, and afterwards at various lower levels above the present valley-plain, in those earlier times when the flint tools of the antique type were buried in successive river beds. I have said at various levels, because there are, here and there, patches of drift at heights intermediate between the higher and lower gravel, and also some deposits, showing that the river once flowed at elevations above as well as below the level of the platform of St.

Acheul. As yet, however, no patch of gravel skirting the valley at heights exceeding 100 feet above the Somme has yielded flint tools or other signs of the former sojourn of Man in this region.

Possibly, in the earlier geographical condition of this country, the confluence of tributaries with the Somme afforded inducements to a hunting and fishing tribe to settle there, and some of the same natural advantages may have caused the first inhabitants of Amiens and Abbeville to fix on the same sites for their dwellings. If the early hunting and fishing tribes frequented the same spots for hundreds or thousands of years in succession, the number of the stone implements lost in the bed of the river need not surprise us. Ice-chisels, flint hatchets, and spear-heads may have slipped accidentally through holes kept constantly open, and the recovery of a lost treasure once sunk in the bed of the ice-bound stream, inevitably swept away with gravel on the breaking up of the ice in the spring, would be hopeless. During a long winter, in a country affording abundance of flint, the manufacture of tools would be continually in progress; and, if so, thousands of chips and flakes would be purposely thrown into the ice-hole, besides a great number of implements having flaws, or rejected as too unskilfully made to be worth preserving.

As to the fossil fauna of the drift, considered in relation to the climate, when, in 1859, I took a collection which I had made of all the more common species of land and freshwater sh.e.l.ls from the Amiens and Abbeville drift, to my friend M. Deshayes at Paris, he declared them to be, without exception, the same as those now living in the basin of the Seine. This fact may seem at first sight to imply that the climate had not altered since the flint tools were fabricated; but it appears that all these species of molluscs now range as far north as Norway and Finland, and may therefore have flourished in the valley of the Somme when the river was frozen over annually in winter.*

(* See Prestwich, Paper read to the Royal Society in 1862.)

In regard to the accompanying mammalia, some of them, like the mammoth and tichorhine rhinoceros, may have been able to endure the rigours of a northern winter as well as the reindeer, which we find fossil in the same gravel. It is a more difficult point to determine whether the climate of the lower gravels (those of Menchecourt, for example) was more genial than that of the higher ones. Mr. Prestwich inclines to this opinion. None of those contortions of the strata above described have as yet been observed in the lower drift. It contains large blocks of Tertiary sandstone and grit, which may have required the aid of ice to convey them to their present sites; but as such blocks already abounded in the older and higher alluvium, they may simply be monuments of its destruction, having been let down successively to lower and lower levels without making much seaward progress.

The Cyrena fluminalis of Menchecourt and the hippopotamus of St. Roch seem to be in favour of a less severe temperature in winter; but so many of the species of mammalia, as well as of the land and freshwater sh.e.l.ls, are common to both formations, and our information respecting the entire fauna is still so imperfect, that it would be premature to pretend to settle this question in the present state of our knowledge.

We must be content with the conclusion (and it is one of no small interest), that when Man first inhabited this part of Europe, at the time that the St. Acheul drift was formed, the climate as well as the physical geography of the country differed considerably from the state of things now established there.

Among the elephant remains from St. Acheul, in M. Garnier's collection, Dr. Falconer recognised a molar of the Elephas antiquus, Figure 19, the same species which has been already mentioned as having been found in the lower-level gravels of St. Roch. This species, therefore, endured while important changes took place in the geographical condition of the valley of the Somme. a.s.suming the lower-level gravel to be the newer, it follows that the Elephas antiquus and the hippopotamus of St. Roch continued to flourish long after the introduction of the mammoth, a well characterised tooth of which, as I before stated, was found at St.

Acheul at the time of my visit in 1860.

As flint hatchets and knives have been discovered in the alluvial deposits both at high and low levels, we may safely affirm that Man was as old an inhabitant of this region as were any of the fossil quadrupeds above enumerated, a conclusion which is independent of any difference of opinion as to the relative age of the higher and lower gravels.

The disappearance of many large pachyderms and beasts of prey from Europe has often been attributed to the intervention of Man, and no doubt he played his part in hastening the era of their extinction; but there is good reason for suspecting that other causes co-operated to the same end. No naturalist would for a moment suppose that the extermination of the Cyrena fluminalis throughout the whole of Europe--a species which co-existed with our race in the valley of the Somme, and which was very abundant in the waters of the Thames at the time when the elephant, rhinoceros, and hippopotamus flourished on its banks--was accelerated by human agency. The great modification in climate and in other conditions of existence which affected this aquatic mollusc, may have mainly contributed to the gradual dying out of many of the large mammalia.

We have already seen that the peat of the valley of the Somme is a formation which, in all likelihood, took thousands of years for its growth. But no change of a marked character has occurred in the mammalian fauna since it began to acc.u.mulate. The contrast of the fauna of the ancient alluvium, whether at high or low levels, with the fauna of the oldest peat is almost as great as its contrast with the existing fauna, the memorials of Man being common to the whole series; hence we may infer that the interval of time which separated the era of the large extinct mammalia from that of the earliest peat, was of far longer duration than that of the entire growth of the peat. Yet we by no means need the evidence of the ancient fossil fauna to establish the antiquity of Man in this part of France. The mere volume of the drift at various heights would alone suffice to demonstrate a vast lapse of time during which such heaps of shingle, derived both from the Eocene and the Cretaceous rocks, were thrown down in a succession of river-channels. We observe thousands of rounded and half-rounded flints, and a vast number of angular ones, with rounded pieces of white Chalk of various sizes, testifying to a prodigious amount of mechanical action, accompanying the repeated widening and deepening of the valley, before it became the receptacle of peat; and the position of many of the flint tools leaves no doubt in the mind of the geologist that their fabrication preceded all this reiterated denudation.

ON THE ABSENCE OF HUMAN BONES IN THE ALLUVIUM OF THE SOMME.