188 Notice of Prof. Forbes s Travels in the Alps. 



We have already made more extensive citations than we intended 

 from this very interesting work, and shall conclude with a few miscel- 

 laneous selections. 



The crevasses of the Mer de Glace were observed to extend two 

 thousand feet, or sometimes half across the glacier, and to be often fif- 

 teen or twenty feet wide, with walls perfectly vertical ; they are evi- 

 dently in some cases formed by the straining of the ice over obstacles ; 

 they begin with a sudden noise, and at first are mere cracks into which 

 the blade of a knife would scarcely enter. They are often obliterated 

 or closed up, especially in winter, and are in a good measure renewed 

 every year, and chiefly in summer, when they frequently undergo a pro- 

 digious enlargement. On the Montanvert there is a moraine two hundred 

 and forty feet above the present glacier, thus proving its former eleva- 

 tion. Professor Forbes found the remains of what was believed to be 

 Saussure's ladder, which he left in the glacier in 1788 ; and comparing 

 dates and distances, it appears to have travelled 16,500 feet in forty- 

 four years, at the rate of 375 feet per annum for the motion of this 

 part of the glacier ; but observations made in other places gave an ap- 

 proximation to five hundred feet in a year. It seems not unreasonable 

 to conclude that the rate of descent may vary in different glaciers. 

 The apparent elevation of rocks by the sinking of the ice around them, 

 has been mentioned. In connection with the medial moraine of the 

 Talafre, there was a very remarkable stone of this description. It was 

 twenty-three feet long by seventeen feet, and three and a half thick. 

 On the 6th of June, 1842, it stood on an elegant pedestal of ice very del- 

 icately poised, and upon this stone the traveller erected his theodolite to 

 make his observations. On the 13th of August, the supporting pedes- 

 tal was thirteen feet high, and soon after the stone slipped from its posi- 

 tion, and in September it was beginning to rise again upon a new icy 

 column, or in other words, the glacier was wasting all around it, and the 

 stone protected the portion on which it reposed, so that it relatively rose. 



A rock that had been smoothly rounded by attrition, was called by 

 Saussure Roche montonnee. 



Near Pont Pelissier such rocks are accompanied by bowlders, " one 

 of which of immense size and angular shape seems poised on the very 

 summit of one of these beehive-like summits ; — rocks so situated are 

 called by De Charpentier blocs perchees. 



" Near St. Gervais are numerous and extensive moraines, although the 

 nearest modern glacier is some hours 1 walk distant. The rocks in place 

 are slaty limestone, but blocs of granite abound, sometimes accumula- 

 ted in ridge-like mounds along the face of the slopes exactly like mo- 

 raines — in other cases insulated and of great size, thirty or forty feet 

 in length ; and they are well characterized protogine or granite of the 



