82 T. BELT Otf THE DRIFT OF DEVON AND CORNWALL. 



the blocks of granite spread over Dartmoor must have been carried by 

 currents of water and floating ice *. The experienced glacialist Mr. J. 

 F. Campbell also believed that the denudation of the tors was due to 

 floating ice f. Many miles to the east, on the Haldon Hills, gravels 

 are found containing pebbles of granite and other crystalline rocks, 

 mingled with chalk flints and chert. At Little Haldon Mr. Mackin- 

 tosh found the gravels 10 feet thick, extending down the sides of 

 the hill, proving that it had its present contour before they were 

 deposited. The top of Little Haldon is about 800 feet above the 

 sea ; and the gravels extend over its summit. 



Gravels with foreign pebbles are found on Straightway Hill, and on 

 the summits of the hills surrounding the vale of Charm outh j. Mr. 

 H. B. Woodward has kindly furnished me with much information 

 respecting the drift-gravels that cover the Black-Down Hills, first 

 described, I believe, by Dr. Buckland. 



The bed-rocks belong to the Greensand formation ; and on the tops 

 of the hills, at heights of from 600 to 700 feet above the sea, occur 

 patches of gravel with large, well-worn boulders of chert, largo 

 pebbles of quartz, rolled flints, and a few boulders of quartzite§. 

 Mr. "Woodward, in a letter to me, says : — " The occurrence of old 

 pebbles iu a clayey drift on the tops of the Greensand heights is the 

 more important because, on the paleozoic rocks of Devonshire, it is 

 often very difficult to decide between a drift gravel and the disin- 

 tegrated conglomerates of the New Red series." 



In Cornwall, upland gravels occur on Crousa Downs, near St. 

 Keverno, and blocks of syenite are spread over the surface of them ||. 

 On the isolated hill of St. Agnes, on the northern coast, Mr. Bene- 

 dict Kitto has described gravels containing angular and waterworn 

 stones covered by clay, and that again by rubble and rounded 

 pebbles %. 



When the nature of the evidence is fully understood, there is not 

 likely to be any difference of opinion respecting the agent that trans- 

 ported the travelled blocks of Devon and Cornwall. The probability 

 that they have been carried by floating ice is great, and is enhanced by 

 the occurrence of rounded pebbles. These require for their forma- 

 tion the presence of water ; and granting the existence of this up to 

 the heights at which they are found, we may easily imagine that, in 

 the Glacial Period, coast ice would form round the shores in winter, 

 and float off pebbles and boulders in the spring. 



b. Lowland deposits. — The Upland deposits are separated from 

 those of lower levels by tracts over which no gravels are now found. 

 They are distinguished from the Lowland deposits by evidence of 

 tranquil deposition, whilst those in the lower grounds occur spread 

 out in wide sheets, exhibiting many signs of sudden and tumultuous 



* Geological Magazine, vol. iv. p. 399. t Frost and Fire, vol. ii. p. 220. 



I Sir H. T. De la Beche, Report on the Geology of Cornwall, p. 395. 

 § Mr. H. B. Woodward, Geological Magazine, 1874, p. 335. 

 || Rev. E. Budge, Trans. Roy. Soc. Cornwall, vol. vi. p. 97 ; and Sir H. T. 

 De la Beche, Report on the Geology of Cornwall, p. 396. 

 ^[ Miners' Assoc. Cornwall and Devon, August, 1874. 



