CLAY-WITH-FLINTS. 43 



To the north and east of South Weald, in the neighbourhood 

 of Brentwood, the Boulder Clay rests in places on the Bagshot 

 Sands and pebble bed. 



The upper part of the pebble-bed, from 3 to 6 ft., consists 

 of re-arranged material with a few quartz pebbles and unworn 

 flints, moved doubtless when ice overspread the land. To that 

 agent, perhaps, the vertical position of the pebbles may be 

 attributed. 1 These features are well seen on the Warley plateau, 

 on the eastern margin of the map. 



More recent downwashes of the Bagshot pebble-beds occur 

 south-east of Great Warley Street, and in places between 

 Brentwood and Brook Street. 



Mixed pebbly flint gravel, with a few pebbles of quartzite, 

 as well as quartz and angular flints, occurs on the border of 

 Dagnam Park, north of Harold Wood, and this is evidently 

 associated with the Boulder Clay. 



No Eolithic or Palaeolithic Implements have been found in 

 any of these Pebble Gravels on the northern side of the Thames. 



CLAY-WITH-FLINTS AND PLATE AU BRICKEARTH. 



On the Chalk tracts of Hertfordshire, Buckinghamshire and 

 the North Downs there occurs an irregular accumulation to 

 which the term Clay-with-flints has been applied. Associated 

 with it there is much brickearth. 



The Clay-with-flints rests generally on a piped surface of the 

 Chalk, and occurs as a lining of reddish brown clay, with unworn 

 flints, often blackened with manganese and iron salts. This 

 portion was largely formed by dissolution of the Chalk liberating 

 the flints, and any insoluble matter in the Chalk. The percentage 

 of earthy matter in the Chalk is, however, very small, and it is 

 admitted that the accumulation represented on the map is a 

 mixed one. 2 



Intermingled with the Clay-with-flints are undoubted relics 

 of Eocene beds ; black flint-pebbles and sand, greywethers, 

 coloured clay, and in some cases considerable tracts of mottled 

 brickearth occur, as well as stones from the Glacial Drift. In 

 mass the accumulation is largely the relic of denudation, locally 

 much modified during successive events of the Pleistocene period. 3 



It is a noteworthy fact that in the Clay-with-flints of the 

 uplands south of Croydon there have been recognised not only 

 flint-pebbles derived from Eocene strata, but chert from the 



1 Woodward, H. B., in ' Geology of London' (Mem. Geol. Surv.}, 1889, p. 273, 

 and Proc. Geol. Assoc., vol. xi, 1889, p. Ixxiii; vol. xviii, 1904, p 486. 

 Monckton, H. W-, and R. S. Merries, ibid., vol. xi, 1889, p. 18; vol. xii, 1892, 

 p. 109. 



2 Whitaker, W., ' Guide to Geology of London ' (Mem. Geol. Surv.), Ed 6, 

 1901, p. 72; Jukes-Browne, A. J., Quart. Journ. Geol. Soc., vol. ] xii, 1906, p. 132. 



3 Sherlock, R. L., and A. H. Noble, ' Glacial Origin of the Clay-with-flints 

 of Bucks.' Quart. Journ. Geol. Soc., vol. Ixviii, 1912, pp. 199-212. 



