226 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



and small crust depressions were exposed where the rocks had 

 offered least resistance to the overlying weight of ice, while 

 large angular blocks were often left in undisturbed position 

 upon the ground-layer of pebble and sand over which the 

 ice-sheet had previously moved. 



A very short time after the appearance of Agassiz' work, 

 Canon Rendu, afterwards Bishop of Annegy, wrote a paper 

 on the physics of glacier ice. He attributed to glacier ice, 

 in spite of its hard and brittle character, a certain ductility 

 which enabled it to mould itself like plastic clay to its 

 surroundings. In this conception Rendu was much in ad- 

 vance of his time, as no observer had thought of any possible 

 connection between plasticity and brittleness. 



In the same year, 1841, Charpentier published his Essai 

 sur les Glaciers, one of the grandest contributions to the 

 geology of his time. This gifted pupil of Werner, whose 

 pioneer researches in the Pyrenees have already been men- 

 tioned, describes in the first part of the essay the pheno- 

 mena of glaciers with a fine precision, rivalling that of 

 Saussure, and with a completeness far beyond any previous 

 contribution on glaciers. He relies almost exclusively upon 

 his own observations, whereas Agassiz frequently used the 

 accounts in the literature. The second part of the essay is 

 even more important. In it erratic blocks are discussed, and 

 the author brings forward a convincing series of facts, from 

 which he draws his conclusion that only glaciers could have 

 transported the blocks and stranded them in their present 

 positions. 



With characteristic modesty, Charpentier claims neither for 

 Venetz nor for himself the authorship of the idea that larger 

 glaciers had formerly filled the Alpine valleys and had left 

 the erratics strewn along them. He relates that uneducated 

 mountaineers, more especially a chamois-hunter, Perraudin, 

 from Lourtier, and a native of Chamonix, Marie Deville, had 

 formed this idea and communicated it orally. He also recalls 

 a remark of Playfair's that had long sunk into oblivion, but 

 was the same in effect as Charpentier's own conclusion. 



The hypothesis of a connected ice-sheet, which had been 

 propounded by Agassiz, was not accepted by Charpentier. In 

 the essay, Charpentier explains his arguments against it, and 

 he further insists that the maximum advance of the glaciers 

 occurred after the upheaval and partial subaerial denudation 



