248 NEOZOIC TIME. [CHAP. XII. 



Weald may then have been occupied by broad plains of 

 Chalk marl and gault, with possibly a small central tract 

 of Lower Greensand and Weald Clay. We may at any 

 rate assume that the present drainage system of the Weald 

 was initiated at that stage in the history of its denudation 

 when such was the condition of its surface, though whether 

 this stage was reached in Miocene, or not until Pliocene 

 time, we are hardly yet in a position to determine. 



From the facts mentioned on p. 235 we may conclude 

 that, after an interval of unknown duration, a general 

 subsidence at length took place, and the period marked by 

 the Miocene deposits commenced. This subsidence brought 

 the shores of a sea which opened southward within a 

 short distance of the British area, if it did not actually 

 invade it. On the south this sea reached to the Cotentin 

 district of Normandy, and on the east it stretched through 

 Belgium to the eastern shore of England. 



Older Pliocene Time. The subsidence which had set in 

 during the formation of the Miocene beds seems to have 

 been continued during that of the older Pliocene, until the 

 whole of south-eastern England was submerged and the 

 sea covered districts which are now more than 600 feet 

 above its level. The remnants of the older Pliocene beds 

 are however so small and scanty, that it is difficult to draw 

 any trustworthy inferences from their distribution regarding 

 the probable limits of the sea in which they were formed. 



The first point which calls for consideration is whether 

 there were two gulfs with an isthmus between them, as in 

 Miocene time, or whether the sea swept across the Channel 

 area and covered the whole of southern England. As re- 

 marked by Mr. Clement Eeid, 1 "a subsidence sufficient to 

 allow only 20 or 30 fathoms of water over the highest 

 parts of the North Downs would submerge the whole of 



1 " Nature," Ang. 12, 1886, p. 342. 



