ALLUVIAL DEPOSITS. 51/ 



Thames Valley Deposits. — The accumulations of gravel in the Thames Valley 

 are of different ages, Pleistocene and Recent. In the higher portions of the 

 valley the gravel is probably for the most part Recent, and it is largely made up oi 

 Oolitic material, as near South Cerney. In the neighbourhood of Oxford the 

 gravel is more mixed in character, and contains much material derived from older 

 Drifts. Thus, in speaking of the gravels at Maidenhead, Prof. Prestwich notes the 

 occurrence of quartzites, etc. , derived originally from the New Red conglomerates 

 of the midland counties, the (lint-pebbles vi'ere mostly derived from Eocene strata, 

 while the subangular Chalk-flints give the measure of the wear and tear to which the 

 stones were subjected when the river-deposit was laid down.^ In some places the 

 Thames Valley sands have been derived from the Tertiary sands. 



Between Oxford and Gravesend the Thames Valley deposits occupy a consider- 

 able area, and especially around .Staines, Colnbrook, West Drayton, Uxbridge, 

 Brentford, Kew, London, and Barking. They rise to an elevation of 154 feet at 

 Highbury Terrace, and 190 feet at Wimbledon. The beds have been divided as 

 follows : - — 



Recent. — Peat and Marsh Clay, etc. (Alluvium). 



'Upper Brickearth, 5 to 20 feet thick. Grays, Erith, Crayford, 

 Wanstead, Tottenham, West Drayton, etc. 

 p, . J Thames Gravel, 12 to 15 feet thick; with bands of sandy 



eis ocene.-! ^j^^ containing freshwater MoUusca at Brentford, Hackney, 



Highbury New Park, etc. 

 .Lower Brickearth, 20 to 30 feet, Ilford, Wickham, etc. 



These divisions of the older Thames Valley-deposits are, however, very local, and 

 although the Brickearth of Grays, Crayford, etc., was regarded by Mr. S. V. Wood, 

 jun., as newer than that of Ilford, there are no marked distinctions between them. 

 Moreover, he regarded the gravel of the Cray and Darent valleys as of the age of 

 the Upper Brickearth. Both Upper and Lower Brickearths contain Corbicula 

 Jluminalis, etc., as well as many Mammalian remains. 



The Thames gravel in its eastern development may be in part estuarine or even 

 marine, especially the portions that border the eastern coast of Essex from 

 Southend and Shoeburyness, northwards by Burnham, and Southminster. The 

 Thames Valley deposits are probably all more recent than the Chalky Boulder 

 Clay ; for that deposit has in no case been found in the valley (see p. 507)> ^"'i 

 the valley gravels contain Grypluca and other derived fossils which have probably 

 been washed out of the Boulder Clay. At the same time these valley-deposits 

 may be older than the Purple and Hessle Boulder Clays of Lincolnshire, etc. 

 (See pp. 481, 49S.) 



Amongst the MoUusca recorded from the Brickearths are Corbicula Jluminalis, 

 Cyclas cornea, Unio litloralis, Planorbis corneus, Paliuiiiia vivipara, Aucylus 

 fiuviatilis, etc. The Mammalia include Fclis spehta, Hyaiia spehra, JJrsus 

 ferox, U. arctos, Canis lupus, Bos primigenius, Bison priscus, Ovibos moschattis, 

 Cerviis megaceros, Elephas, Rhinoceros, Hippopotamus, Castor, etc. (See list, 

 p. 477.) Many Palajolithic Implements have been found associated with these 

 Mammalia. 



In the British Museum there is a tooth of the Mammoth found in 1731, at a 

 depth of 28 feet beneath the surface in digging a sewer along Pall Mall. A more 

 interesting record is the finding of an old flint implement and the tooth of a 

 Mammoth {before 1 715) near Grays Inn Lane. Palaeolithic Implements and fresh- 

 water shells have also been found in the gravels of Hackney Down, Shacklewell, 

 in the brickearth of Highbury New Park, and other places.^ 



^ Q. J. xii. 131 ; Phillips, Geol. Oxford, etc., p. 456. 



2 S. V. Wood, jun. G. Mag. 1866, pp. 57, 99, 106 ; Ibid. 1868, p. 534 ; W. B. 

 Dawkins, Q. J. xxiii. 91, xxxvi. 379 ; A. Tylor, G. Mag. 1868, p. 391 ; Morris, 

 Q. J. vi. 201 ; Prestwich, Q. J. xi. 107 ; Goodchild, P. Geol. Assoc, ix. 151. 



^ J. E. Greenhill, P. Geol. Assoc, viii. 336, and Prehistoric Hackney, Hackney 

 Micros, and Nat. Hist. Soc. 1881-83. 



