REVIEWS. 



339 



again declined ; and the terminal moraines of tlie Blione glacier, arranged con- 

 centrically one within anotlier, bear witness to its recent gradual diminution. 

 The great Gonier glacier of Monte Rosa, also, is even now steadily advancing, 

 and is said within the memory of men not old, to have already swallowed up 

 forty chalets and a considerable tract of meadow-land. But all such historical 

 variations in the magnitude of glaciers are trifling compared with their wonder- 

 ful extension in pre-historic periods. There is, perhaps, scarcely a valley in the 

 High Alps in wliich the traveller, whose eye is educated in glacial phenomena, 

 will not discern symptoms of the former presence of glaciers where none now 

 exist ; and in numerous instances, far from requniug to be searched for, these 

 indications force themselves on the attention by signs as strong as if the 

 glacier had disappeared but a short time before the groT^^h of the living vege- 

 tation. So startling indeed, are these revelations, that for a time the observer 

 scarcely dares to adniit to himseK the justness of Ms conclusions, when he finds 

 in striations, morames, roches moutonnees and blocs perches unequivocal marks of 

 the former extension of an existing glacier more than a long day's march 

 beyond its present termmation ; and further, that its actual surface of to-day is 

 a thousand feet and more beneath its ancient level." 



As it is with the glaciers of the Aar, which the professor selects as examples, 

 so is it wath many other alpine vaUeys, and so has it been in North Wales. 

 After this follow interestmg observations on the disappearance of moraines, 

 the former state of the Grmisel, the Aletech glacier, the Kirchet, on the inter- 

 esting question whetlier a glacier ever reached the Jura? and on the great 

 perched blocks of Monthey, one of them twenty paces in length, and eight 

 thousand or nine thousand tons in weio-ht. 



These blocks lie in great quantities in and upon sandy gravel roughly strati- 

 fied, comparable more in their semi-angular cliaracter to the partially-rounded 

 challc-flints of our ordinary " diift" gravels. " Similar drift-like strata encircle 

 the Lake of Geneva, rising high above its level, and thence range across the 

 low lands of Switzerland, at the base of the Jura towards Zurich and Schaff- 

 hausen, covering the hills hundi-eds of feet above the level of the lakes of 

 Zurich and Zug, each of which lies more than a hundred feet above the Lake of 

 Geneva. 



"If this view of the subject be correct," it is argued, "it follows that 

 during part of the period when the North of Europe was submerged to receive 

 the di'ift, Switzerland also lay beneath the sea, at least two thousand feet 

 beneath its present level, that being about the height of the blocks of Monthey 

 above the sea." 



The ancient glacial phenomena of Switzerland are then shown to accord with 

 those of North Wales ; and the tract between the Snowdon range and the 

 Menai Straights is described, in which we are favoured ^^dth examples of hlocs 

 perches, roches moutonnees, erratic blocks, polished and striated rocks, and 

 moraines, by which the region of Snowdon is brought prominently before us as 

 the site, in geological and pre-historic times, of mighty glaciers, of which the 

 only evidences that now remain are the inscriptions they have themselves en- 

 graven, ages since, in their irresistible passage. 



Snowdon, the highest and noblest mountam of the district, " is bounded on 

 three sides by six vast hoUows or vaUeys, which have been scooped out from 

 time to time in the rock-masses of which the mountain is formed. In one of 

 these, Cwm-glas, some of the most perfect remains of glacier-action are to be 

 found in the form of moraine-debris and heaps of clay, boulders, and angular 

 blocks identical in composition and in general aspect with the Swiss moraines." 



Professor Ramsay then proceeds with others of these vaUeys describing their 

 beauties and their evidences of ancient glacial phenomena, coming to the con- 

 clusion that Snowdon formed the centre of six glaciers having an ice-thickness 



