184 Mr. Darwin on the Ancient Glaciers of Caernarvonshire, 



that sea-shells have been found on Moel Faban, two miles 

 N.E. of Bethesda. I ascended this and some neighbouring 

 hills, but could find no trace of any deposit likely to include 

 shells. This hill stands isolated, out of the course of the gla- 

 ciers from the central valleys ; it exceeds 1000 feet in height; 

 its surface is jagged, and presents not the smallest appear- 

 ance of the passage of glaciers : but high up on its flanks (and 

 perhaps on its very summit) there are large, angular and 

 rounded boulders of foreign rocks. 



Along the sea-coast between Bangor and Caernarvon, and 

 on the Caernarvonshire plain, I did not notice any boss-formed 

 hillocks of rock. The whole country is in most places con- 

 cealed by beds of till and stratified gravel, with scattered 

 boulders on the surface: some of these boulders were scored. 

 From the account given by Mr. Trimmer* of his remarkable 

 discovery of broken fragments of Buccinum, Venus, Natica, 

 and Turbo, beneath twenty feet of sand and gravel, on Moel 

 Tryfan (S.E. of Caernarvon), I ascended this hill. Its height 

 is 1192 feetf above the sea; it is strewed with boulders of fo- 

 reign rock, most of them apparently from the neighbouring 

 mountains ; but near the summit I found the rounded chalk- 

 flints X and small pieces of white granite alluded to by Dr. 

 Buckland. Its form is conical, and it stands isolated: 

 wherever the bare rock protrudes its surface is jagged, and 

 shows no signs of being in any part worn into bosses. The 

 contrast between the superficial part of the bare rock on this 

 hill and on Moel Faban, with that of the rocks within the 

 great central valleys of Caernarvonshire, is very remarkable ; 

 it is a contrast of precisely the same kind as may be observed 

 in these same valleys by ascending on either side above the 

 reach of the ancient glaciers. A little way down the hill, a 

 bed two or three feet in thickness, of broken fragments of slate 

 mixed with a few imperfectly rounded pebbles and boulders 

 of many kinds of rock, is seen in several places to rest on the 

 slate, the upper surface of which, to the depth of several feet, 

 has been disintegrated, shattered and contorted in a very cu- 

 rious manner. The laminated fragments, however, sometimes 

 partially retain their original position. 



I did not succeed in finding any fragments of shells, but 

 near the summit of the hill on the eastern or inland side, I 

 found beds, at least twenty feet in thickness, of irregularly 

 stratified gravel and boulders, with distinct and quite defined 

 layers of coarse yellow sand, and others of a fine argillaceous 



• Proceedings of the Geological Society, vol. i. p. 332. [Phil. Mag. loc. cit.] 

 t Murchison's Silurian System, p. 528. 



j I may mention, that at Little Madely, in Staffordshire, I have found 

 chalk-flints in the gravel-beds, associated with existing species of sea-shells. 



