3 1 2 English Formations. 



part of the land through which the river flowed that 

 deposited the Wealden and Purbeck beds, they were 

 undergoing constant waste, so that in the course of time, 

 having been previously tilted upwards to the west with 

 an eastern dip (fig. 59), they were worn into what I 

 have elsewhere termed a plain of marine denudation 

 (see p. 497). The submergence of the Wealden area 

 was followed by the progressive sinking of the Oolitic 

 and older strata further west, so that, as the successive 

 members of the Cretaceous formations were deposited, 

 it happened that by slow sinking of the land, the Upper 

 Cretaceous strata gradually overlapped the edges of the 

 outcropping Oolitic and Liassic formations, till at length 

 they were intruded on the New Eed series, and even on 

 the Palaeozoic strata of Devonshire itself, as shown in 

 fig. 59. 



The upheaval of the Chalk into land brought this 

 epoch to an end, and those conditions that contributed 

 to its formation ceased in our area. As the uppermost 

 member of the Upper Secondary rocks, it closes the 

 record of Mesozoic times in England. 



This brings us to the last divisions of the British 

 strata which I shall now name. These were deposited 

 on the Chalk, and are termed Eocene formations (No. 

 12, fig. 57, p. 304). At the base they consist of marine 

 and estuary deposits, known as the Thanet Sand, and 

 Woolwich and Reading beds, and which are of compara- 

 tively small thickness, say from 50 to 150 feet. These 

 lie below the London Clay and form the outer border of 

 the London basin. The Woolwich and Reading beds 

 are found in the Isle of Wight, and in part constitute 

 the Hampshire and London basins. In these we 

 have in places the same kind of alternations of fresh- 



