1 PLIOCENE. 39 



small faults in the Eocene strata are more nearly allied to land- 

 slips and die out in the lower beds ; they have been observed at 

 Nunhead, Lewisham, Blackheath, Croydon and elsewhere. 1 In 

 the London Clay such slips, though frequent, cannot be seen 

 in sections. In Wimbledon an excavation seen in 1912 showed 

 18 ft. of London Clay, apparently in situ, but beneath it was a 

 garden soil yielding relics of the early 18th century. At Brock- 

 well Hall Brickyard, where the Peabody Buildings now stand, 

 Mr. Whitaker noted a section in which small faults, clearly seen 

 in the bedded sands, are not traceable in the homogeneous 

 London Clay above ; in the same district a remarkable case of 

 ' overfolding,' probably superficial in character, was revealed in 

 1921, when the cutting on the L.B.S.C. Railway south of New 

 Cross was cleaned. 2 



A small reversed fault, bringing Reading Beds against London 

 Clay, was met with in the Tube Railway between Oxford Circus 

 and Regent's Park. 3 



CHAPTER VI. 



PLIOCENE (AND LATER). 



The folding described in the previous chapter, though it 

 began during the deposition of the Eocene Beds, was in the 

 main post-Eocene ; it appears to have been practically com- 

 pleted during the Oligocene and Miocene periods, but it is highly 

 probable that movement, better described as a tilt, caused a 

 general submergence of this part of England in the late Miocene 

 or early Pliocene 4 (Diestian,) period. 



About 8 miles south of St. George's Hill, Wey bridge, there 

 occur at Netley Heath, on the Chalk of the North Downs, certain 

 patches of yellow sand 5 to 12 ft. thick, with a few flint-pebbles, 

 and ferruginous sandy and occasionally glauconitic grit; here 

 Mr. W. P. D. Stebbing discovered casts of fossils; 5 further finds 

 have since been made 6 but the state of preservation does not 

 permit specific identification. Some 12 genera occur, of which 

 11 are also found in the Lenham Beds which belong to the 

 Diestian 7 . The strata occur at an altitude of 570 to 600 ft. 



1 ' Geology of London ' (Mem. Geol. Surv.), vol. i, 1889, pp. 130, 158, 

 231, etc. 



2 Bromehead, C. N., Proc. Oeol. Assoc., vol. xxxiii, 1922, pp. 77, 78, Plate IV. 



3 ' Summary of Progress for 1905 ' (Mem. Oeol Surv.), 1906, p. 168. 



4 The term ' Pliocene ' is used here and by the writers quoted in the sense 

 of ' contemporary with the Lenham Beds ' ; Mr. R. B. Newton now considers 

 that the Diestian division to which these beds belong is more correctly referred 

 to the Upper Miocene. See Journ. ConchoL, vol. xv, 1916, pp. 56-149. 



5 Proc. Oeol. Assoc., vol. xvi, 1900, pp. 524-526. 



6 Ibid., vol. xxviii, 1917, p. 50. 



7 Reid, C., ' Pliocene Deposits of Britain ' (Mem. Oeol. Surv.), 1890, pp. 42-58. 



