OLDER GRAVELS. 41 



as ' Plateau Gravel of various ages ' ; but the same division 

 includes certain gravelly accumulations which do not contain 

 the foreign material and are presumably older. The other two 

 divisions, ' Clay-with-flints ' and ' Plateau Brickearth,' are con- 

 fined to the Chalk areas ; they merge into one another and are of 

 mixed character and indefinite age. The Boulder Clay and 

 Glacial Gravels are discussed in the next chapter, but we are 

 now concerned with the remaining parts of the l Plateau Gravel/ 

 the Plateau Brickearth and Clay-with-flints. These deposits 

 are all destitute of contemporaneous organic remains and some 

 may possibly represent decalcified relics of Diestian or later 

 Pliocene strata. They occur at higher levels than those locally 

 reached by the Glacial Gravels, usually round about 400 ft. 



THE OLDER GRAVELS. 



North of the Thames these ancient gravels are best seen, 

 within our area, on Stanmore Hill, at Oxhey Wood, Totteridge 

 and around Chipping Barnet. At Stanmore Hill Mr. B. W. 

 Pocock finds that ' Reading pebbles form by far the greater 

 part of the hard material, and many of these appear to have 

 been weathered before being involved in this deposit. Vein- 

 quartz is fairly common . . . and occurs as small pebbles, 

 only one specimen above an inch long having been found. Other 

 pebbles are very rare. A few of the flints have been derived 

 directly from the Chalk, and prolonged search yielded one or 

 two fragments of cherty rock (possibly from the Lower Green- 

 sand), one well-rounded pebble of sarsen and one fairly large 

 block of a pebbly variety of the same.' 1 At Barnet both the 

 quartz pebbles and the chert are more abundant. Mr. Pocock 

 notes the important fact, that, though patches of this high level 

 gravel occur to the north-west, the chert is practically limited 

 in that direction by a line running from a short distance north 

 of Barnet to Little Berkhampstead. 2 This suggests that the 

 chert was derived from the Wealden area rather than from that 

 north of the Chilterns. 3 The reverse appears to be true of the 

 quartz pebbles, which are extremely abundant in the Lower 

 Greensand at Leighton Buzzard and elsewhere in the northern 

 outcrop. 4 



At Little Heath, 5J miles north of our north-west corner, 

 Mr. C. J. Gilbert claims to have discovered a shore-deposit of 

 these gravels. 5 He considered the gravels to be of Pliocene 

 age and marine origin, on the latter point having the support of 

 McKenny Hughes: 6 



1 ' Summary of Progress for 1913 ' (Mem. Oeol. Surv.), 1914, p. 33. 



2 * Summary of Progress for 1914 ' (Mem. Oeol. Surv.), 1915, p. 33. 



3 Quart. Journ. Oeol. Soc., vol. Ixxv, 1920, pp. 49, 50. 



4 Barrow, G., ibid., p. 45. 

 6 Ibid., pp. 32-43. 



6 Quart. Journ. Qiol. Soc. t vol. xxiv, 1868, pp. 233-237. 



