﻿part 1] RIVER-GORGES IN CORNWALL AND DEVON. 73 



locality, and, as it is the only wide extent of level ground in the 

 neighbourhood, it has been utilized for the erection of reservoirs. 

 Mr. Reid was of opinion that the flat is cut in the Bovey Beds. 

 The deposits at the locality are mainly sand and gravel, and 

 resemble those found at St. Agnes Beacon. 



Conclusions. 



(1) In North Cornwall, near Tintagel, there is an area charac- 



terized by peculiar topographical features, namely : — a 

 widespread plateau terminating inland at a height of 430 feet 

 above sea-level, against a degraded line of cliffs, and dissected 

 by deep ravines into flat-topped blocks of land. In these 

 ravines the rivers flow as rapids and cascades, and sometimes 

 end as coastal waterfalls, leaping over the cliff's edge into 

 the sea. Everywhere in the walls of these ravines remnants 

 of ' marmites ' are preserved, while the rivers swirl among 

 the existing potholes. 



(2) These topographical features are repeated elsewhere in Corn- 



wail, and also in Devon at numerous localities ; but such 

 localities are separated one from the other by regions 

 characterized by differed - ^aphical features. 



(3) Wherever the ^ 1 " J ..rved. it is dissected by valleys 



with steep _ frequently ravines or gorges through 

 which the rivers flow as rapids and cascades and often in 

 potholes. 



(4) These facts suggest causal relationship between the two groups 



of natural features, and, if the development of the valleys 

 be traced, it is seen that they owe their origin to the rejuven- 

 escence of the rivers following upon the uplift of the plateau. 

 In the Tintagel country the rivers fell as waterfalls over the 

 cliff's edge and rapidly ripped out chasms for themselves by 

 means of potholes, many remnants of which are preserved, 

 while others are being formed. In other districts gorges 

 were formed by the shortening of the river-courses owing 

 to the annexation of their head-waters by other streams 

 through breaches made in the valley-sides. 



(5) The formation of these ravines is subsequent to the Pliocene 



Period, and resulted from enhanced erosive powers of the 

 rivers brought about by elevation of the land. 



EXPLANATION OF PLATES V-VII. 

 Plate V. 



A sea-breached valley at Lundy Beach, St. Minver. The valley has been 

 breached by the sea undercutting- the cliff, leaving remnants of its western 

 bank. It formed part of a drainage-system, now submerged under the sea, 

 which extended along the northern coast of Cornwall, between the estuary of 

 the Camel and Tintagel. (See p. 64.) 



Q. J. Gr. S. No. 285. g 



