44 LONDON DISTRICT. 



Hythe Beds, and ferruginous sandstone possibly from the 

 Folkestone Beds of the Lower Greensand. 1 



Plateau or Eolithic implements have been found near Shore- 

 ham, Eynsford and other places where Clay-with-flints is shown 

 on the map. 



Good examples of the deep hollows or ' pipes ' -filled with 

 gravel and Clay-with-flints are met with in the cuttings of the 

 Metropolitan Railway beyond Bickmans worth, and elsewhere. 

 In these pipes the chalk walls are usually lined with Clay-with- 

 flints, while the middle part is filled with an accumulation of 

 material derived from the strata which locally overlie the Chalk ; 

 examples of pipes filled with Blackheath Beds at Worms Heath, 

 four miles south of Addington, have recentlv been described by 

 Mr. Whitaker. 2 



CHAPTER VII. 



PLEISTOCENE. 



GLACIAL DEPOSITS. 



The Glacial Deposits shown on the map include the Boulder 

 Clay, found about Finchley and in Essex, and the gravels 

 coloured pink other than those just described. These gravels 

 are in part older and in part newer than the Boulder Clay ; those 

 at Finchley underlie this deposit and have been termed ' Middle 

 Glacial ' as they are newer than the Lower Glacial Drift of 

 Norfolk. They were probably formed by flood-water, due to 

 the melting of the ice before it reached our area from the north ; 

 owing to an increase of cold or some other change the ice-cap 

 then advanced into the Thames Valley, and the Boulder Clay 

 was laid down beneath it. With the return of more clement 

 conditions the ice again melted and newer gravels were formed 

 in the same way as before. Unless, therefore, Boulder Clay is 

 preserved beneath or above the gravels, it is difficult to say 

 whether a particular mass is earlier or later than the maximum 

 glaciation. Both series are characterised by the occurrence in 

 fair abundance of liver-coloured quartzite pebbles derived from 

 the Bunter, by many erratic rocks, some of Scandinavian origin, 

 by fossils derived from Jurassic and other formations, as well as 

 by quartz, chert, flints, ironstone, blocks of sarsen stone and 

 puddingstone, of more or less local origin. Contemporary 

 fossils have not been found within the district, nor are any 

 implements recorded from beneath the Boulder Clay. 



1 Quart. Journ. Geol. Soc., vol. xlvii. 1891, pp. 127-54; and Proc. & Trans. 

 Croydon Micros. & Nat. Hist. Club, 1896-7, 1897, p. 219. 



2 Quart. Journ. GeoL Soc., vol. Ixxv, 1920, pp. 7-31. 



