TRANSACTIONS OF THE SECTIONS. 127 



and even the Petherwin beds, than with the Carboniferous ; hence they may be 

 considered as belonging rather to the last than to the Devonian series, or possibly 

 they may have to be regai-ded as "Passage beds " between them. 



On the Age of the Granites of Dartmoor. By "W. Pengelly, F.Q.S. 



It has long been well known that the Dartmoor granites have sent veins into 

 the cidmiferoiis rocks of North and Central Devon, and that the latter are much 

 bent and contorted, probably by the intrusion of the former*; consequently the 

 granites are more modem than the rocks they have thus invaded and disturbed. 



Geologists, however, are by no means agTeed respecting the age of the granites 

 relatively to that of the deposits of the coimty more modem than the culmiferous 

 beds. Sir H. De la Beche regards them as more ancient than the red conglomerates 

 and sandstones of South Devon, but says, " The evidence is not always so clear as 

 could be desired ; for among all the pebbles of the red conglomerate extending from 

 Torbay to Exeter, we have not been able to detect any portion of it, though the 

 granite ranges so near that part of the red conglomerate. In the tongaie of red 

 sandstone and conglomerate which runs from Crediton by North Tawton and Samp- 

 ford Courtney to Jacobstow, we have, however, detected pebbles like some varieties 

 of Dartmoor granite f." This is certainly not a very pronounced opinion in favour 

 of this evidence ; in another place, however, he speaks somewhat more decidedly 

 in fovour of the pebbles J ; but he appears to base his chronological opinion mainly 

 on the fact that the red sandstone series ai'e foimd resting quietly on the basset 

 edges of the upturned cidmiferous beds§. 



Mr. Godwin- Austen, however, is of a different opinion. " As no granite pebbles," 

 he says, " have been found among the various materials of which the new red con- 

 glomerate is composed, we may conclude that at the period of its accumulation the 

 granite of Dartmoor coidd not have been exposed, particularly when we bear in mind 

 that the two formations are at present separated only by the valley of the Teigii. 



" The beds of the Greensand of the Haldous and the Bovey Valley, in the thin 

 mica, sharp quartzose crystals and seams of felspar, suggest that they may have re- 

 sulted from a decomposed granite district ; but here, again, although fragments of 

 all the older rocks occur in the conglomerate beds at the base of the Greensand, 

 granitic pebbles are altogether wanting ; nor do we meet with them until we anive, 

 in ascending order, at those superficial accumidations which cap the ITaldons. Pos- 

 sibly, then, the rise of the gi'.anite of Dartmoor in its present form may belong to a 

 period comparatively modem ||". 



Happening a few years ago to be at North Tawton, I mentioned the subject to 

 Mr. Wm. Vicaiy, then resident there, who at once took me to the conglomerate, 

 and in a very few minutes extracted two or three pebbles, which we both regarded 

 as of Dartmoor derivation. Whether they were strictly granite in the technical 

 sense of the word may possibly be questioned ; and it is certain that much of the 

 granitic mass of Dartmoor will not pass muster as true granite^ ; but that the pebbles 

 foiuid at North Tawton were of Dartmoor extraction, and can be matched bythousands 

 in the rivulets and torrent-com-ses of the Moor, I have no manner of doubt. 



In August 1861 I met Mr, Vicary at Exeter, where he now resides, and again 

 spoke of the Tawton pebbles. He infonned me that he had found unmistakeable gi'a- 

 nite pebbles in the red conglomerate at the base of Ilaldon, a well-known hill about 

 five miles south of Exeter. He also iufomied me that since his discovery his 

 attention liad been called to the fact that Mr. Brice, in his 'History of Exeter,' 

 mentions the occuiTence of pebbles of granite in the red conglomerate at Haldon**. 



We at once started for the spot, and passing through Alphiugton and Kennford, 



* Sir H. De la Bcche's "Eeport," p. 16.5; Professor Sedgwick and Sir R. I. Murchison 

 in Geol. Trans, vol. v. pt. 3. p. 686-7 ; Mr. Godwin-Austen, Geol. Trans, vol. vi. pt. 2. 

 p. 477 ; and Mr. Ormcrod in Quart. Joiu-u. Geol. Soc. vol. sv. p. 492. 



t Report, p. 166. 



J Mem. Geol. Survey, vol. i. p. 228. 



§ Eeport, ]). 166; see also 'Geol. Observer,' p. 648. 



II Geol. Trans, vol. vi. pt. 2. p. 478. 



•ii See Sir H. De la Becbe's "Report," p. 158. 



«» History of Exeter, by Thomas Brice, 1802, p. 114. 



