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 A HISTORY OF KENT thickness, of loam and reddish-brown clay full of unworn flints, which has accumulated deeply in the little ' pipes ' and hollows of the rock and to a less extent on the intervening spaces. It is believed that this ' Clay- with-Flints ' represents the insoluble matter remaining from the gradual decay and lowering of the Chalk under the action of surface waters, mixed here and there with a Httle detritus from Tertiary beds that once existed at higher levels. Occasionally also patches of water-worn gravel are found at high elevations, of uncertain origin but probably the relics of long-vanished streams whose gathering grounds have been carried away by the recession of the escarpments. Great interest has been aroused in these high-level deposits of the Downs ^ by the discovery of large numbers of weathered flints with rudely chipped edges, supposed to be of human workmanship and of older date than the ' Paleolithic ' implements found in the gravels of lower levels, and therefore named ' eoliths.' The artificial character of these ' eoliths ' is denied by some authorities, and the subject will require further investigation before it can be regarded as settled.^ River Drift. — The older river deposits of the main valleys consist of terraces of gravel, sand and flood-loam or brick-earth, that often occur at levels high above the present streams and mark successive stages in the deepening of their channels. These beds have been care- fully studied in Kent, and much has been written regarding them ; but space-limits forbid more than a brief mention here of the chief exposures. Below Woolwich, where the Darent joins the Thames, the slopes are bordered by a thick mass of fossiliferous brick-earth, inter- stratified with sand and gravel, into which large pits have been dug between Erith and Crayford. Besides numerous land and freshwater shells, the remains of mammoth, elephant, rhinoceros, hippopotamus, lion, bear, wolf, hyena, bison, bos, musk-ox, elk, stag, horse and many smaller animals, including the Norwegian and the Arctic lemmings,^ have been obtained from these excavations,* and also coarsely-chipped Paleolithic flint implements, undoubted relics of ancient man. In one of the pits at Crayford flint flakes were scattered plentifully in a well- defined layer, and this was proved to be an actual working-place of the old implement-makers in chipping flint ' baches,' as in one case when the contiguous flakes were collected it was found possible to replace them in their relative positions so that the outline of the original unworked 1 The gravels of this district and the age of the flint implements have been discussed in detail by the late Prof. J. Prestwich in the following papers : 'On the Occurrence of Palaeolithic Flint Imple- ments in the neighbourhood of Ightham, Kent,' Quart. Journ. Geo/. Soc. (1889), xlv. 270 ; ' On. . . a Southern Drift in the Thames Basin ..." ibid. xlvi. 155; ' On the Age, Formation and Successive Drift Stages of the Darent Valley,' ibid. (1891), xlvii. ; 'Flint Implements of the Chalk Plateau of Kent,' Joun. Anthrop. Inst. (1892), p. 24 ; and in Controverted Questions o/Geo/ogy, London, 870(1895), pp. 49-81, etc. See also W. Cunnington, 'On some Palaeolithic Implements from the Plateau Gravels, and their evidence concerning " Eolithic" Man,' Quart. Journ. Geo/. Soe. (1898), Ivi. 291. 2 For further discussion of these ' eoliths,' see the article on ' Early Man ' in this volume. 3 E. T. Newton, ' On the occurrence of Lemmings, etc., in the Thames Valley,' Geo/. Mag. (1890), dec. 3. vii. 452. 22
 * For further details, see article on ' Palaeontology,' p. 31.