606 SCIENCE PROGRESS 



implements in considerable numbers and in various localities 

 in these gravels of the great southern drift at an elevation of 

 750 ft. above the sea-level. These discoveries led Professor 

 Prestvvich to institute an exhaustive inquiry as to these upland 

 drifts ; and the startling conclusion he arrived at is that the 

 oldest of them, the great southern drift, in which the imple- 

 ments are found, could have come only from a mountain range 

 2,000 to 3,000 ft. high, which formerly ran from east to west in 

 the line of the anticlinal axis, which runs down the centre to the 

 present Weald of Kent, between the North and South chalk 

 Downs, and which has since worn down to the present low 

 forest-ridge by sub-aerial denudation " (the italics not in the 

 original). 



" The reasoning by which this inference is supported seems 

 irresistible. The drift could not have been deposited by the 

 present rivers, or during the present configuration of the 

 country, for it is found at levels 300 ft. to 400 ft. higher than 

 the highest watersheds between the existing valleys. It 

 consists not only of chalk flints, but to a great extent of chert 

 and sandstones, such as are found at present in the forest- 

 ridge of the Weald and nowhere else. It must have been 

 brought by water, for the gravels are to a considerable extent 

 rounded and waterworn. Judging from the size of the rolled 

 stones, this water must have travelled with considerable 

 velocity ; and it must have come from the south, because the 

 cherts and grits are found only there, and because the levels 

 at which the gravels are found are in that direction. By 

 following these levels as far as the present surface extends, 

 which is to the southern edge of the greensand, it is easy to 

 plot out what must have been the continuation of this rising 

 gradient to the south, and what the elevation of the southern 

 range, in which these northward-flowing streams took their 

 origin. Prestwich has gone into the question in full detail, 

 and his conclusion is that the height of this wealden ridge 

 must have been at least 2,800 ft., or, in other words, that about 

 2,000 ft. must have disappeared by denudation. 



" This is the more conclusive because Prestwich approached 

 the subject with a bias towards shortening rather than lengthen- 

 ing the periods commonly assigned for the glacial epoch and 

 the antiquity of man. 



Underground Erosion 



From the following it will be seen that the official view 

 has not yet accepted the idea of subterranean erosion. 



In Ightham : The Story of a Kentish Village, Mr. F. J. 

 Bennett, inserted as an addendum, p. 130 : 



