440 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 22, 



like that of Dartmoor, more deeply seated. The dynamical effects on 

 the slate rocks which occupy the interval between Salcombe and the 

 Dartmoor granite at South Brent and Ivy Bridge would still be much 

 the same, as there is pretty good evidence to show that all these 

 great granitic masses of Devon and Cornwall belong to one epoch *, 

 and have been the direct cause which has brought the slaty rocks 

 into their present position. 



V. Geanite of Dartmooe axd of Beown Willy (Camelford). 



The Dartmoor granite has been also fully described by Sir Henry 

 De la Beche f, Sir Roderick Murchisou and Prof. Sedgwick :f, Mr. 

 Godwin- Austen §, and other writers of earlier date. It will be suf- 

 ficient, therefore, for my present purpose merely to restate the rela- 

 tions these masses bear to the surrounding rocks, in order that their 

 influence in bringing about the general disposition of the latter, 

 above described, may not be overlooked. 



The Dartmoor granite has pressed the Culm-measures to the 

 northward, bringing the beds into nearly vertical positions. On the 

 east, between Dunsford and Bovey Tracey, it has broken through the 

 beds, which range up to it more or less at right angles to its margin^ 

 and the volcanic rocks interstratified with them are altered and ren- 

 dered crj'stalline. South of Bovey Tracey, however, and thence 

 to Skeriton, the granite throws the Culm-measures off to the south- 

 east. At its southern extremity, near Ivy Bridge, it has broken 

 through the Devonian rocks ; but around Cornwood the latter form a 

 shallow basin between the granite at Harford and the offstanding 

 protruding mass of Crown Hill Down. Westward of Crown Hill 

 Down, and, in fact, along the whole south-western border of Dart- 

 moor, as far as Meav}^, the granite has broken through the bed- 

 ding, which trends up to its edge ; but thence northwards, almost to 

 Bridestow, the beds dip away from the granite at for the most part 

 low angles, and occasionally they are nearly horizontal, as in the 

 neighbourhood of Petertavy. 



The granite of the Camelford Hills throws off the beds to the 

 south, which dip at moderate angles towards Liskeard. On the 

 north it has carried the beds which range up from the north of Hing- 

 ston Down to the north-east, and beds on the same geological hori- 

 zon dip off the granite on the west at tolerably high angles. Lower 

 beds, however, are brought up on the east and north-west of the 

 granite. Those on the east dip away from its margin somewhat 

 iiTcgulaiiy ; those on the north-west stretch away towards Cadon 

 Barrow, thromng off higher beds to the north-east and west. 



The rocks contiguous to the granite are altered by it ; and the 

 resulting metamorphic rock, of course, varies with the original con- 

 stitution of the rock acted upon. Generally the effects are very feeble 

 at a distance of a .quarter of a mile from its margin ; but it extends 

 further where the beds dip off from the granite than where they 



* See also on tliis point Sedgwick and Murchison, I. c. p. 685, and De la 

 Beche, Kep. p. 165. 



t Eep. p. 157 et seq. t L. c. p. 685. § L. v. p. 476. 



