8o GEOLOGY OF THE ISLE OF WIGHT 



the gravel has somehow flowed. The sharp wall in which 

 it ends at the upper part of the slope shows that it once 

 extended to the south over ground since worn away. 

 Clearly, the gravel was formed before denudation had cut 

 out the great gap between the central and southern downs 

 of the Island. The down where the gravel lies is 363 ft. 

 above sea level, 313 ft. above the bottom of the valley 

 below. So that, though the gravel sheet is much newer 

 than the strata we have been studying, it must neverthe- 

 less be of great antiquity. 



It seems that at the top of St. George's Down we are 

 standing on what was once the floor of an old valley. In 

 the course of denudation the bottom of a river valley 

 often becomes the highest part of a district. For the bed 

 of the valley is covered by flint gravel, and flint is ex- 

 cessively hard, and the bed of flints protects the under- 

 lying rock ; so that, while the rocks on each side are worn 

 away, what was the river bed is eventually left high 

 above them. Thus the highest points of a district are 

 often capped by flint gravel marking the beds of old 

 streams. Tracing up this old valley to the southward, 

 at a few miles distance it will have reached the chalk 

 region on the south of the anticline : and the flints carried 

 down the valley may have come from beds of angular 

 flints already dissolved out of the chalk such as we find 

 on St. Boniface Down. 



But how have these great masses of flints been swept 

 along ? Can the land have been down under the sea ; 

 and have sea waves washed the stones along ? But these 

 flints, though water-worn, are not rounded as we find 

 beach shingle. What immense rush of water can have 

 spread these flints 30 feet deep along a river valley ? 

 We must go to mountain regions for torrents of this 

 character. And then, mountain torrents round the stones 

 in their bed while these are mostly angular. The history 

 of these gravels is a difficult one. I can only give what 



