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The alluvium of the Seine and its tributaries, like that of the Somme, contains no fragments of rocks brought from any other hydrographical basin; yet the shape of the land, or fall of the river, or the climate, or all these conditions, must have been very different when the grey alluvium in which the flint tools occur at Paris was formed. The great size of some of the blocks of granite, and the distance which they have travelled, imply a power in the river which it no longer possesses. We can hardly doubt that river-ice once played a much more active part than now in the transportation of such blocks, one of which may be seen in the Museum of the École des Mines at Paris, three or four feet in diameter.

Post-pliocene Alluvium of England, containing Works

of Art. In the ancient alluvium of the basin of the Thames, at moderate heights above the main river, and its tributaries, we find fossil bones of the same species of extinct and living mammalia, accompanied by recent species of land and freshwater shells, as we have shown to be characteristic of the basins of the Somme and the Seine. We can scarcely therefore doubt that these quadrupeds, during some part of the postpliocene period, ranged freely from the continent of Europe to England, at a time when there was an uninterrupted communication by land between the two countries. The reader will not therefore be surprised to learn that flint implements of the same antique type as those of the valley of the Somme have been detected in British alluvium.

The most marked feature of this alluvium in the Thames valley is that great bed of ocbreous gravel, composed chiefly of broken and slightly worn chalk flints, on which a great part of London is built. It extends from above Maidenhead through the metropolis to the sea, a distance from west to east

CHAP. IX.

POST-PLIOCENE ALLUVIUM OF ENGLAND.

155

of fifty miles, having a width varying from two to nine miles. Its thickness ranges commonly from five to fifteen feet.* Interstratified with this gravel, in many places, are beds of sand, loam, and clay, the whole containing occasionally remains of the mammoth and other extinct quadrupeds. Fine sections have been exposed to view, at different periods, at Brentford and Kew Bridge, others in London itself, and below it at Erith in Kent, on the right bank of the Thames, and at Ilford and Gray's Thurrock in Essex, on the left bank. The united thickness of the beds of sand, gravel, and loam amounts sometimes to forty or even sixty feet. They are for the most part elevated above, but in some cases they descend below, the present level of the overflowed plain of the Thames.

If the reader will refer to the section of the post-pliocene sands and gravels of Menchecourt, near Abbeville, given at p. 122, he will perfectly understand the relations of the ancient Thames alluvium to the modern channel and plain of the river, and their relation, on the other hand, to the boundary formations of older date, whether tertiary or cretaceous.

So far as they are known, the fossil mollusca and mammalia of the two districts also agree very closely, the Cyrena fluminalis being common to both, and being the only extra-European shell, this and all the species of testacea being recent. Of this agreement with the living fauna there is a fine illustration in Essex; for the determination of which we are indebted to the late Mr. John Brown, F.G.S., who collected at Copford, in Essex, from a deposit containing bones of the mammoth, a large bear (probably Ursus spelous), a beaver, stag, and aurochs, no less than sixty-nine species of land and fresh-water shells. Forty-eight of these were terrestrial, and two of them, Helix incarnata and H. ruderata, no longer inhabit the British Isles, but are still living on the continent, ruderata in high northern latitudes.* The Cyrena fluminalis and the Unio littoralis, to which last I shall presently allude, were not among the number.

* Prestwich, Geological Quarterly Journal, vol. xii. p. 131.

I long ago suggested the hypothesis, that in the basin of the Thames there are indications of a meeting in the postpliocene period of a northern and southern fauna. To the northern group may have belonged the mammoth (Elephas primigenius) and the Rhinoceros tichorhinus, both of which Pallas found in Siberia, preserved with their flesh in the ice. With these are occasionally associated the rein-deer. In 1855 the skull of the musk-ox (Bubalus moschatus) was also found in the ochreous gravel of Maidenhead, by the Rev. C. Kingsley and Mr. Lubbock; the identification of this fossil with the living species being made by Professor Owen. A second fossil skull of the same arctic animal was afterwards found by Mr. Lubbock near Bromley, in the valley of a small tributary of the Thames; and two other skulls, those of a bull and a cow were dug up near Bath Easton from the gravel of the valley of the Avon by Mr. Charles Moore. Professor Owen has truly said, that, as this quadruped has a constitution fitting it at present to inhabit the high northern regions of America, we can hardly doubt that its former companions, the warmly-clad mammoth and the two-horned woolly rhinoceros (R. tichorhinus), were in like manner capable of supporting life in a cold climate.'t

I have alluded at p. 153 to the recent discovery of this same buffalo near Chauny, in the valley of the Oise, in France; and in 1856 I found a skull of it preserved in the museum at Berlin, which Professor Quenstedt, the curator, had correctly named so long ago as 1836, when the fossil was dug out of drift, in the hill called the Kreuzberg, in the southern

* Quarterly Geological Journal, he merely meant extinct in England. vol. viii. p. 190, 1852.

See also Jeffreys, Brit. Conch. p. 174. Mr. Brown calls them extinct species, + Geological Quarterly Journal which may mislead some readers, but vol. xii. p. 124.

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suburbs of that city. By an account published at the time, we find that the mammalia which accompanied the musk buffalo were the mammoth and tichorhine rhinoceros, with the horse and ox;* but I can find no record of the occurrence of a hippopotamus, nor of Elephas antiquus or Rhinoceros leptorhinus, in the drift of the north of Germany, bordering the Baltic.

On the other hand, in another locality in the same drift of North Germany, Dr. Hensel, of Berlin, detected, near Quedlinburg, the Norwegian Lemming (Myodes Lemmus), and another species of the same family called by Pallas Myodes torquatus(by Hensel, Misothermus torquatus)—a still more arctic quadruped, found by Parry in latitude 82°, and which never strays farther south than the northern borders of the woody region. Professor Beyrich also informs me that the remains of the Rhinoceros tichorhinus were obtained at the same place.f

As an example of what may possibly have constituted a more southern fauna in the valley of the Thames, I may allude to the fossil remains found in the fluviatile alluvium of Gray's Thurrock, in Essex, situated on the left bank of the river, twenty-one miles below London. The strata of brickearth, loam, and gravel exposed to view in artificial excavations in that spot, are precisely such as would be formed by the silting up of an old river channel. Among the mammalia are Elephas antiquus, Rhinoceros leptorhinus (R. megarhinus, Christol), Hippopotamus major, species of horse, bear, ox, stag, &c., and, among the accompanying shells, Cyrena fluminalis, which is extremely abundant, instead of being scarce, as at Abbeville. It is associated with Unio littoralis, fig. 22, also in great numbers, and with both valves united. This conspicuous fresh-water mussel is no longer an inhabitant of

* Leonhard and Bronn's Jahrbuch, 1836, p. 215.

+ Zeitschrift der Deutschen Geolo

gischen Gesellschaft, vol. vii. 1855, p. 497, &c.

the British Isles, but still lives in the Seine, and is still more abundant in the Loire. Another fresh-water univalve (Paludina marginata, Michaud), not British, but common in the

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Unio littoralis, Gray's Thurrock, Essex; extinct in British Isles,

living in France.

south of France, likewise occurs, and a peculiar variety of Cyclas amnica, which by some naturalists has been regarded as a distinct species. With these, moreover, is found a peculiar variety of Valvata piscinalis.

If we consult Dr. Von Schrenck's account of the living mammalia of Amoorland, lying between lat. 45° and 55° North, we learn that, in that part of North-Eastern Asia recently annexed to the Russian empire, no less than thirty-four out of fifty-eight living quadrupeds are identical with European species, while some of those which do not extend their range to Europe are arctic, others tropical forms. The Bengal tiger ranges northwards occasionally to lat. 52° North, where he chiefly subsists on the flesh of the rein-deer, and the same tiger abounds in lat. 48°, to which the small tail-less hare or pika, a polar resident, sometimes wanders southwards.*. We may readily conceive that the countries now drained by the Thames, the Somme, and the Seine, were, in the post-pliocene

* Mammalia of Amoorland, Natural History Review, vol. i. p. 12, 1861.

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