﻿part 1] RIVER-GORGES IN CORNWALL AND DEVON. 71 



a ravine exceeding 200 feet in depth. Its abandoned valley is still 

 impressive on account of its depth and breadth, and because of 

 the craggy hills bounding it at Was Tor and Brentor. 



The relative period when the diversion occurred is determinable 

 by the relationship of the river to the neighbouring features. The 

 gorge extends from a waterfall (Kitt's Steps) for a distance of 

 some 2 miles, and rests in an older, wider valley. The bottom 

 of this older valley is nearly 700 feet above sea-level ; its slopes 

 pass gradually into a general plateau-feature (well shown by the 

 contours on PI. VII), probably of the age of a similar plateau 

 on Bodmin Moor and described by Mr. Barrow 1 as the 7 50-foot 

 plateau. 



That is to say, the old river had eroded a valley in this plateau 

 to a depth of 50 feet, when its waters gained enhanced cutting- 

 power by an increased gradient arising from a shortening of their 

 journey to the lowlands. So rapidly has the Lyd flowered its bed 

 that a tributary now joins it as a waterfall issuing from a hanging 

 valley (at the point X on PI. VII) and leaping in two bounds, the 

 last over 100 feet clear into the Lyd valley. 



The gorge is merely a narrow cleft or chasm sawn through the 

 grits and shales of the Cuhn Measures, and in places only a few 

 feet wide. Its walls are riddled with ancient potholes, best seen, 

 perhaps, near Lydford Bridge, and representing the drill-holes 

 made by the river in deepening its channel. 



The map (PI. VII) shows the course of the Lyd before its 

 western bank was 1 breached by the lateral stream. From Lydford 

 a profile view of the ancient valley can be seen. On the west, the 

 slopes of it are conspicuous near Raddon and Was Tor, while 

 the eastern bank extends by Watervale Farm and thence south- 

 wards past Black Down towards St. Mary Tavy. The western 

 bank at Lydford Junction is much steeper, on account of its having 

 been undercut by the river impinging against the hard igneous 

 mass of Was Tor. The valley beyond (now followed by two lines 

 of railway) is wide though nearly dry, but is obviously the work 

 of a river much more powerful than the existing puny stream that 

 flows along it. 



The recent valley at the gorge is graven in the older one, the 

 bed of the river being nearly 250 feet lower, but following the same 

 course to a point near Was Tor, where it makes a right-angle bend 

 and then trends nearly due west for several miles. At the point 

 where the river turns to the west a V-shaped cleft has been cut in 

 the ancient valley- slopes, a feature which is conspicuous when viewed 

 either from the high land near Watervale or from down-stream, 

 looking eastwards up the valley. 



Eastern Dartmoor. 



On Eastern Dartmoor there are equally significant and con- 

 spicuous features indicating the former existence and wide extent 



1 Q. J. Gr. S. vol. lxiv (1908) pp. 384-400. 



