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XXX.. Notes on the Effects produced by the Ancient Glaciers 

 of Caernarvonshire, and on the Boulders transported by 

 Floating Ice. By Charles Darwin, Esq., M.A., F.R.S. 

 and F.G.S. 



#?j_UIDED and taught by the abstract of Dr. Buckland's 

 ^ memoir " On Diluvio- Glacial Phaenomena in Snowdonia 

 and the adjacent parts of North Wales*," I visited several of 

 the localities there noticed, and having familiarized myself 

 with some of the appearances described, I have been enabled 

 to make a few additional observations. 



Dr. Buckland has stated that a mile east of Lake Ogwyn 

 there occurs a series of mounds, covered with hundreds of 

 large blocks of stone, which approach nearer to the condition 

 of an undisturbed moraine, than any other mounds of detritus 

 noticed by him in North Wales. By ascending these mounds 

 it is indeed easy to imagine that they formed the north-west- 

 ern lateral moraine of a glacier, descending in a north-east line 

 from the Great Glyder mountain. But at the southern end 

 of Lake Idwell the phenomena of moraines are presented, 

 though on a much smaller scale, with perfect distinctness. 

 On entering the wild amphitheatre in which Lake Idwell lies, 

 some small conical, irregular little mounds, which might easily 

 escape attention, may be seen at the further end. The best 

 preserved mounds lie on the west side of the great black per- 

 pendicular face of rock, forming the southern boundary of the 

 lake. They have been intersected in many places by streams, 

 and they are seen to consist of earth and detritus, with great 

 blocks of rock on their summits. They at first appear quite 

 irregularly grouped, but to a person ascending any one of 

 those furthest from the precipice, they are at once seen to 

 fall into three (with traces of a fourth) narrow straight linear 

 ridges. The ridge nearest the precipice runs someway up the 

 mountain, but the outer one is longer and more perfect, and 

 forms a trough with the mountain-side, from 10 to 15 feet deep. 

 On the eastern arid opposite side of the head of the lake, cor- 

 responding but less developed mounds of detritus may be seen 

 running a little way up the mountain. It is, I think, impossi- 

 ble for any one who has read the descriptions of the moraines 

 bordering the existing glaciers in the Alps ; to stand on these 

 mounds and for an instant to doubt that they are ancient mo- 

 raines ; nor is it possible to conceive any other cause which 

 could have abruptly thrown up these long narrow steep mounds 

 of unstratified detritus against the mountain-sides. The three 



* Read before the Geological Society, December 15th, 1841, and the 

 Abstract is published in the Athenaeum, 1842, p. 42. [An Abstract of Dr. 

 Buckland's paper, from the Proceedings of the Society, will appear in an 

 early number of the Philosophical Magazine.— Edit.] 



