GEOLOGY 



IN Devon the south-western peninsula of England attains its greatest 

 breadth from the Foreland on the shores of the Bristol Channel to 

 Prawle Point on the English Channel, a distance of y^ miles. From 



this axis of greatest breadth the distance between the Channels 

 decreases eastward to about 35 miles from Sidmouth northward. This 

 expansion of the peninsula includes the highest land in England south of 

 Derbyshire ; the Exmoor highlands on the north, and the tor-crowned 

 hills of Dartmoor on the south, being for the most part above the 1,000 

 feet contour. An orographical map distinguishing heights of, and over, 

 1,000 feet brings these uplands of west Somerset and Devon in line with 

 the mountainous areas of Wales. 



The eastern border of the Welsh highlands if prolonged to Watchet 

 and from thence southward across the Devon and Somerset boundary 

 and by Exeter and Chudleigh to Newton Abbot and Torquay, divides 

 Devon into two areas differing in their physical features and geological 

 structure. The western area comprises north, central and south Devon. 

 It is composed of older rocks than those in the eastern area, and exhibits 

 a more diversified surface with bolder hills and narrower valleys. 



The westerly trend of the rolling hill ranges of Exmoor is main- 

 tained throughout north Devon, the general summit-level declining 

 southward and rising again toward Dartmoor. 



To the south of Dartmoor the summits are much lower and the 

 higher features run westward from Staddon Heights, near Plymouth, 

 to Southdown Cliff and Scabbacombe Head on the coast south of 

 Berry Head. 



In the Start and Bolt districts the scenery is grander than on any 

 other part of the Devon coast ; this is due to the rugged character of 

 the rocks rather than to altitude, as the height rarely exceeds 400 feet. 



The western area is drained by the rivers Taw, East and West 

 Okement, Teign, Dart, Avon, Erme and Yealm, all of which rise in 

 the highlands of Dartmoor ; by the Torridge and Tamar with sources 

 not far from Hartland Point on the north coast ; and near its eastern 

 margin by the Exe and its tributaries. 



In the eastern area the Blackdowns, from 500 to 800 feet in height, 

 and the Haldons, from 700 to 800 feet, are the dominant elevations. 

 They are disconnected portions of a great tableland, or peneplain, which 

 once doubtless extended over the whole of the eastern area, and has been 

 breached and cut back to its present limits by the river Exe and its 

 tributaries the Culm and Clyst, and by the Otter, Sid and Axe. 



