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RIVER- GOUGES IN CORNWALL AND DEVON. 



G3 



•5. On the Origin of some River-Gorges in Cornwall and 

 Devon. By He^ry Dewey, F.C.S. (Read February 23rd, 

 1916.) 



[Plates V-VII.] 



The river-gorges here described are situated for the greater part 

 in North Cornwall, between Boscastle and Tregardock, though a 

 few occur in other parts of Cornwall and in Devon. Some of the 

 characteristics of the coastal gorges of Devon have already been 

 described by Dr. E. A. N. Arber, 1 but there appear to be additional 

 features in those of North Cornwall, which are possibly due to 

 their mode of origin. 



These gorge-like valleys are more or less restricted to areas of 

 peculiar topography, and their origin is connected with the history 

 of that topography; while they form a sharp contrast with the 

 valley- sj^stems where such a topography does not exist. Thus, 

 the valley- systems of Cornwall are divisible into two groups, each 

 being marked by features peculiar to it ; although in some cases 

 the river-valley exemplifies the two types of scenery in different 

 parts of itself. 



The difference is in part due to their respective stages of develop- 

 ment, but mainly marks a renewal or rejuvenescence of the rivers' 

 activity. The fall of these rivers near Tintagel averages 1 foot in 

 every 13 feet. 



The gorges are incised in an upland plain, which truncates all 

 hills at a uniform height of about 430 feet above the level of the 

 sea, while the other series of valleys lies in an area diversified by 

 many irregular hills and buried and submerged estuaries. 



The Upland Plain. 



This feature has become well-known in Cornwall through 

 Clement Reid's 3 descriptions. It is everywhere bounded landwards 

 by a prominent ridge, marking a range of degraded cliffs, which 

 also form the boundary of the hills rising above it to a height 

 of 1000 feet above sea-level. This planation has affected alike 

 rocks of different degrees of hardness, reducing them all to a level 

 surface, and cutting a notch in the higher ground beyond them. 

 When viewed in profile, and especially from places a few miles 

 away, this feature is very conspicuous, as when the Tintagel 

 country is seen from Pentire Head, or the Land's End from Carn 

 Brea. 



From Boscastle the plain is continuous for several miles towards 

 the south, where, at Tregardock, the sea has encroached on the 



1 ' The Coast Scenery of North Devon ' London, 1911. 



2 I desire to place on record here how greatly I am indebted to the late 

 Mr. Clement Eeid, for valuable hints and encouragement received from him 

 during some seven years of joint field-work in Cornwall and elsewhere. 



