202 NEOZOIC TIME. [CHAP. XI. 



Bagshot Beds are chiefly sands with intercalated layers of 

 clay. There is generally a complete passage by gradually 

 increasing sandiness, or by such alternations from one 

 formation to the other. In these beds plant remains are 

 the only fossils found. 



The London Clay attains its greatest thickness (480 feet) 

 in Essex and Kent, where the Lower Bagshots are thin, 

 and it must have spread over a large area to the north as 

 well as to the south of its present limits, for a boring so 

 far north as Yarmouth passed through 310 feet of it; 

 originally, therefore, it must have covered the greater 

 part, if not the whole, of Norfolk, and doubtless extended 

 far beyond the present line of the chalk escarpment 

 in Suffolk, Herts, .Bucks, and Oxford. When traced 

 westward through the London basin the clay becomes 

 gradually thinner. Thus, in the Bagshot and Aldershot 

 country it is only about 330 feet thick, but the beds 

 grouped as Lower Bagshot are here from 120 to 150 feet 

 thick, so that the total still reaches 480 feet. Moreover, at 

 Kamsdell, near Basingstoke, there is a mass of brown clay 

 30 feet thick in what are called Lower Bagshot Beds, but 

 the only reason for not calling this London Clay is the 

 presence of sand below it. 



When traced westward from the longitude of Eeading 

 and Basingstoke, the whole of the Lower Eocene under- 

 goes such a rapid change and thinning out that we seem to 

 be approaching a shore-line in that direction, and we cer- 

 tainly find the limit of the area in which the London Clay 

 was formed. 



Writing on the " Western End of the London Basin " in 

 1862, l Mr. Whitaker showed that near Marlborough the 

 London Clay is reduced to a thickness of 15 feet, but is 

 covered by a certain thickness perhaps 40 or 50 feet of 

 " Lower Bagshot " Beds ; still further west the basement 

 1 "Quart. Journ. Geol. Soc.," vol. xviii. p. 259. 



