RIVER DEPOSITS. 51 



thickness the brickearth varies from a few feet to 20 ft. or more. 

 Hydrated oxide of manganese is not uncommon in the Thames 

 V 7 alley gravels, where it is found, usually in association with 

 ferric oxide, coating grains of sand and pebbles and forming 

 black or blue-black seams. 1 



FOSSILS. 



In a general sense the great mass of the Valley Gravel and 

 brickearth belongs to the later Pleistocene period, when man 

 occupied the district in association with a fauna, many of 

 the members of which are extinct or no longer inhabitants of 

 this country. 



Brentwood, Uphall, and Ilford, West Thurrock and Grays 

 (just beyond the limits of the map), Crayford and the Swans- 

 combe area are the more noted localities where mammalian 

 remains have been found in abundance, a fact which may be attri- 

 buted for the most part to the extensive excavations made to 

 obtain brickearth and gravel. 



It is not possible in this work to give lists of fossils which 

 characterise any one horizon or terrace exclusively, but certain 

 general remarks may be made. The fauna of the oldest (Boyn 

 or 100-ft.) terrace indicates a fairly warm climate; in the middle 

 (Taplow or 50-ft.) many of the same forms survive, but others 

 indicative of a colder climate appear, such as the reindeer and 

 the musk-sheep (Ovibos moschatus Zimm.); so far as is known, 

 the latter is confined to this horizon. In the lowest (Flood-plain) 

 terrace the reindeer attains its acme, and the period represented 

 has been termed by some writers ' the age of the reindeer.' 2 



The elephants, whose remains are among those most frequently 

 found, do not afford much help ; in the Thames and Somme 

 Valleys Elephas antiquus, a warm -climate form, generally charac- 

 terises the Boyn Terrace, being succeeded by the mammoth, 

 but in Belgium the latter occurs in the earliest and in South 

 France the former survives till the latest of the Palaeolithic 

 deposits. 3 



Beds containing remains of arctic plants have been found at 

 several localities in, and especially near the base of, the Flood - 

 plain gravels, 4 accompanied by mollusca and other fossils from 

 which also a cold climate may be inferred. The physical 

 characters of certain valley deposits also point to a cold period 

 immediately following the 'deposition of the Taplow gravels 



iHudleston, W. H., and F. G. H. Price, Proc. Geol. Assoc., vol. iii, 1872, 

 pp. 52-55; Hinton, M. A. C., Sci. Gossip, N.S. vol. vi, 1899, p. 146; Johnson, 

 J. P., Essex Nat,, vol. xii, 1901, p. 133. See also Mackie, W., Geol. Mag., 1902, 

 p. 558. 



2 e.g. Wood, S, V., Junr., Quart. Journ. Geol. Soc., vol. xxxviii, 1882, 

 pp. 712-732, and many continental authors. 



3 ' Guide to the Antiquities of the Stone Age,' British Museum, 2nd Edition, 

 1911, pp. 43, 44. 



4 Abbott, W. J. L., Proc. Geol. Assoc., vol. xii, 1892, pp. 346-356. Warren 

 S. H , Quart. Journ. GeoL Soc., vol. Ixviii, 1912, pp. 213-251. 



