CHAP. XI.] HANTONIAN PERIOD. 199 



south of the Weald, near Brighton, it is as much as 958 

 feet. 



I agree with Dr. Barrois in thinking that the highest 

 zones of the Chalk do not exist beneath the London area, 

 but entirely differ from his view that their absence is due 

 to original non-deposition. I see no reason to doubt that 

 such an oceanic deposit as the uppermost Chalk extended 

 continuously from Kent to Norfolk, and that its present 

 absence near London is the result of pre-Tertiary erosion. 



The lowest Eocene group, the Lower London Tertiaries, 

 as they are sometimes called, is a somewhat complex one. 

 The lowest member (Thanet Beds) is in East Kent about 

 80 feet thick, and consists chiefly of sandy marl or 

 clay passing up into grey sand, with layers of calcareous 

 sandstone ; westward these beds are replaced by sharp 

 grey or buff sand, which is 40 feet thick near Woolwich, 

 but thins westward through Surrey, and has not been 

 traced continuously further than Leatherhead. Beneath 

 the London Clay they extend as far as Chertsey, and thence 

 the boundary appears to run north-east along a line by 

 Hampstead, Enfield, Epping, and Braintree, to beyond 

 Sudbury. The Thanet Sands are therefore limited to the 

 eastern part of the London basin. 



The next subdivision is known as the Woolwich and 

 Reading Beds, and is a very variable set of deposits, but 

 has a much wider extension, for it occurs throughout the 

 London and Hampshire basins, and seems to have been 

 continuous originally across the intervening chalk ridges of 

 Hampshire. These beds exhibit three distinct types or 

 facies, and the geographical position and extent of these 

 types is of course an important consideration. 



1. The first and most widely distributed type is that of 

 the Reading Beds, which prevail throughout the central 



to the thickness of chalk pierced by the boring. For this and other 

 information on these borings I am indebted to Mr. VVliitaker. 



