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MAMMALS OF AMOORLAND.

CHAP. IX.

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

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.

CHAP. IX.

CHRONOLOGY OF FLUVIATILE DEPOSITS.

159

period, on the borders of two distinct zoological provinces, one lying to the north, the other to the south, in which case many species belonging to each fauna endowed with migratory habits, like the living musk-buffalo or the Bengal tiger, may have been ready to take advantage of any, even the slightest, change in their favour to invade the neighbouring province, whether in the summer or winter months, or permanently for a series of years, or centuries. The Elephas antiquus and its associated Rhinoceros leptorhinus may have preceded the mammoth and tichorhine rhinoceros in the valley of the Thames, or both may have alternately prevailed in the same area in the post-pliocene period.

In attempting to settle the chronology of fluviatile deposits, it is almost equally difficult to avail ourselves of the evidence of organic remains and of the superposition of the strata, for we may find two old river-beds on the same level in juxta-position, one of them perhaps many thousands of years posterior in date to the other. I have seen an example of this at Ilford, where the Thames, or a tributary stream, has at some former period cut through sands containing Cyrena fluminalis, and again filled up the channel with argillaceous matter, evidently derived from the waste of the tertiary London clay. Such shiftings of the site of the main channel of the river, the frequent removal of gravel and sand previously deposited, and the throwing down of new alluvium, the flooding of tributaries, the rising and sinking of the land, fluctuations in the cold and heat of the climate- all these changes seem to have given rise to that complexity in the fluviatile deposits of the Thames, which accounts for the small progress we have hitherto made in determining their order of succession, and that of the imbedded groups of quadrupeds. It may happen, as at Brentford and Ilford, that sand-pits in two adjoining fields may each contain distinct species of elephant and rhinoceros; and the fossil remains in both cases

160

CHRONOLOGY OF FLUVIATILE DEPOSITS.

CHAP. IX.

be

may occur at the same depth from the surface, yet may severally referable to different parts of the post-pliocene epoch, separated by thousands of years.

The relation of the glacial period to alluvial deposits, such as that of Gray's Thurrock, where the Cyrena fluminalis, Unio littoralis, and the hippopotamus seem rather to imply a warmer climate, has been a matter of long and animated discussion. Patches of the northern drift, at elevations of about two hundred feet above the Thames, occur in the neighbourhood of London, as at Muswell Hill, near Highgate. In this drift, blocks of granite, syenite, greenstone, coal-measure sandstone with its fossils, and other palæozoic rocks, and the wreck of chalk and oolite, occur confusedly mixed together. The same glacial formation is also found capping some of the Essex hills farther to the east, and extending some way down their southern slopes towards the valley of the Thames. Although no fragments washed out of these older and upland drifts have been found in the gravel of the Thames containing elephants' bones, it is fair to presume that the glacial formation is the older of the two, for reasons given before at p. 130, and that it originated, as we shall see in a future chapter, when the greater part of England was submerged beneath the sea. In short, we must suppose that the basin of the Thames and all its fluviatile deposits are post-glacial, in the modified sense of that term; i. e. that they were subsequent to the marine drift of the central and northern counties, and to the period of its emergence above the level of the sea.

Having offered these general remarks on the alluvium of the Thames, I may now say something of the implements hitherto discovered in it. In the British Museum there is a flint weapon of the spear-headed form, such as is represented in fig. 8, p. 114, which we are told was found with an elephant's tooth at Black Mary's, near Gray's Inn Lane, London. In a letter dated 1715, printed in Herne's edition of 'Leland's

CHAP. IX. FLINT IMPLEMENTS IN MIDDLESEX AND SURREY. 161

Collectanea,' vol. i. p. 73, it is stated to have been found in the presence of Mr. Conyers, with the skeleton of an elephant.* So many bones of the elephant, rhinoceros, and hippopotamus have been found in the gravel on which London stands, that there is no reason to doubt the statement as handed down to us. Fossil remains of all these three genera have been dug up on the site of Waterloo Place, St. James's Square, Charing Cross, the London Docks, Limehouse, Bethnal Green, and other places within the memory of persons now living. In the gravel and sand of Shacklewell, in the north-east district of London, I have myself collected specimens of the Cyrena fluminalis in great numbers, see fig. 17 c, p. 124, with the bones of deer and other mammalia.

In the alluvium also of the Wey, near Guildford, in a place called Pease Marsh, a wedge-shaped flint implement, resembling one brought from St. Acheul, by Mr. Prestwich, and compared by some antiquaries to a sling-stone, was obtained in 1836 by Mr. Whitburn, four feet deep in sand and gravel, in which the teeth and tusks of elephants had been found. The Wey flows through the gorge of the North Downs at Guildford to join the Thames. Mr. Austen has shown that this drift is so ancient that one part of it had been disturbed and tilted before another part was thrown down.†

Among other places where flint tools of the antique type have been met with in the course of the last three years, I may mention one of an oval form found by Mr. Whitaker in the valley of the Darent, in Kent, and another which Mr. Evans found lying on the shore at Swalecliff, near Whitstable, in the same county, where Mr. Prestwich had previously described a fresh water deposit, resting on the London clay, and consisting chiefly of gravel, in which an elephant's tooth and the bones of a bear were embedded. The flint implement

* Evans, Archæologia, 1860.

Quarterly Geological Journal, 1851, vol. vii. p. 278.

M

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FLINT IMPLEMENTS IN KENT.

CHAP. IX.

was deeply discoloured and of a peculiar bright light brown colour, similar to that of the old fluviatile gravel in the cliff.

Another flint implement was found in 1860, by Mr. T. Leech, at the foot of the cliff between Herne Bay and the Reculvers, and on further search five other specimens of the spear-head pattern so common at Amiens. Messrs. Prestwich and Evans have since found three other similar tools on the beach, at the base of the same wasting cliff, which consists of sandy Eocene strata. Upon these, at the top of the cliff, is a pebbly deposit of fresh-water origin, about fifty feet above the sea-level, from which the flint weapons must have been derived. Such old alluvial deposits now capping the cliffs of Kent seem to have been the river-beds of tributaries of the Thames before the sea encroached to its present position and widened its estuary. On following up one of these fresh-water deposits westward of the Reculvers, Mr. Prestwich found in it, at Chislet, near Grove Ferry, the Cyrena fluminalis among other shells.

The changes which have taken place in the physical geography of this part of England during, or since, the postpliocene period, have consisted partly of such encroachments of the sea on the coast as are now going on, and partly of a general subsidence of the land. Among the signs of the latter movement may be mentioned a fresh-water formation at Faversham, below the level of the sea. The gravel there contains exclusively land and fluviatile shells, of the same species as those of other localities of the post-pliocene alluvium before mentioned, and must have been formed when the river was at a higher level and when it extended farther east. At that era it was probably a tributary of the Rhine, as represented by Mr. Trimmer in his ideal restoration of the geography of the olden time. For England was then united to the continent, and what is now the German Ocean was

* Quarterly Geological Journal, vol. ix. pl. 13, No. 4.