232 Physical Geography. 



instance derived from him, subsequently aided by 

 personal observation on the ground. 



The story revealed by these various strata is this : 

 When, after the temporary upheaval of the Lower Green- 

 sand, the land gradually sank in part beneath the sea, 

 it happened that the Upper Greensand was being 

 deposited far in the west on a sea-bottom that now forms 

 an eastern part of Devonshire. Not far from its margin, 

 a fragment of the old greater land, in our day known in 

 a modified form as the granite hills of Dartmoor, stood 

 high above the level of the sea, and at the same time, 

 on the opposite side of what is now the Bristol Channel, 

 Wales also formed high land. The pebbly shore of the 

 lower land near Dartmoor, has long ago been destroyed 

 by denudation, but the sediments laid down not far 

 from the shore still exist in the coarse sandy strata that 

 form the Upper Greensand west and east of the river 

 Exe. As we go eastward from that area towards 

 Devizes, the Upper Greensand still continues to be com- 

 paratively coarse, and by degrees in Buckinghamshire, 

 and Bedfordshire, and on into Cambridgeshire, it gets 

 finer and finer, and at length becomes white, calcareous, 

 and marly, and, as it were, seems to mingle with the 

 Gault beneath and the Chalk above, and the Gault, 

 indeed, in a lithological point of view, sometimes seems 

 to disappear altogether. 



In like manner, at the western end of the Wealden 

 area, and along the base of the South and North Downs, 

 the Upper Greensand for many miles consists of fine, 

 white sand, and in the Malm-rock is somewhat chalk-like 

 and calcareous, till going further east towards Folkestone, 

 it gradually becomes untraceable as a special formation, 

 and merges into the underlying Gault and the over- 

 lying Chalk. 



