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 GEOLOGY brickfield, on the right hand side of the lane leading from Ilford to Barking, a spot about twenty-eight feet above the river Thames. 1 The mammals include fine examples of the mammoth or Elepbas primigenius, also E. antiquus, the hippopotamus, three species of rhino- ceros, the Irish elk, bison, urus, red deer, brown bear, grisly bear, wolf and many others. A few flint implements have likewise been found. Occasional remains of birds and fishes, and numerous land and freshwater mollusca also occur in the brickearth, a deposit laid down under more tranquil conditions than the gravel, and due largely to the destruction of Eocene beds and Drift sands and loams. The gravel has been derived mainly from pre-existing gravels formed of flint, with less abundant quartz and quartzite. The flint pebbles were derived from Eocene pebble-beds, and the sub-angular flints, quartz and quartzite mainly from the Boulder Clay or from old plateau or Glacial gravels which border the Thames valley from near Great Marlow to Rickmansworth, Hendon and Finchley. Occasional greywethers occur, as at Grays. 1 The sheets of gravel and brickearth which extend from Southend and Shoeburyness northwards to Great Wakering, Burnham, Southmin- ster and Bradwell, and occur also on Osea Island, may originally have been connected with the tracts around Clacton and Little Holland. In- deed, it is considered that in old times the Thames turned northwards along the eastern margin of Essex, receiving the Blackwater as a tribu- tary. In this region its right bank has been wholly lost by the subse- quent waste of the land on that side. Thus the Thames was a much mightier river than it is now, but when we contemplate the broad ex- panse occupied by the old valley gravels and brickearths, we need not conclude that the river ever occupied, unless in seasons of flood, the entire area. Its tendency has been to alter its course, and, as pointed out by Mr. Whitaker, for the most part to diverge towards the south, so as to cut against the Kentish shores, while leaving broad tracts of loam and gravel to the north. 8 It is difficult to say whether the land was higher or lower during the earlier stages of the formation of these valley deposits, if we accept the view that the lower terraces are of later age where the river cut deeper into the valley. On this subject opinions differ. The land originally may have been much higher, and the river, more or less torrential, cut deeper and deeper into its valley before reach- ing a base-level of erosion. In other valleys there are deposits of river gravel, as along the Colne at Dedham village, and the Cam at Wenden and Great Chester- 1 See Catalogue of the Pleistocene Vertebrata from the neighbourhood of Ilford, Etiex, in tin Colkction of Sir Antonio Brady, by William Davies, 8vo, London, 1874 ; also Henry Woodward, Geol. Mag., 1864, p. 241, 1868, p. 540 ; and M. A. C. Hinton, Proc. Geol. Assoc., vol. xvi. p. 177. 1 For details relating to Grays see B. B. Woodward, Proc. Geol. AIIOC., vol. xi. pp. 363, 364 (herein are references to the labours of all previous workers) ; see also Prestwich, Geol. Mag., 1898, p. 409. Whitaker, Geology of London, vol. i. pp. 353, 496 ; Ramsay, Quart. Journ. Geol. Sot., vol. xxviii. p. 148 ; Prestwich, ibid. vol. xlvi. p. 155 ; J. W. Gregory, Natural Science, vol. v. p. 97. i 17 3
 * For a review of the literature of the Thames Valley Drift and of the origin of the Thames, see