20 The Life and Writings of Agassiz. 



at the period when the blocks now found at a distance from 

 the glaciers were first detached, the glaciers themselves must 

 have reached farther than at present. 



These notions, however, had not extended beyond the limits 

 of the Alpine valleys ; M. Venetz, an engineer of the Valais, 

 was the first to undertake an application of them, in a trea- 

 tise on the subject, in which he shewed that, at various pe- 

 riods, since the end of the last century, the glaciers had ex- 

 tended farther than at present, and, in retiring, had left every- 

 where heaps of stones and large rocks as marks of their pre- 

 sence. Afterwards, M. de Charpentier conceived the idea of 

 extending the application of these facts beyond the region of 

 the present glaciers. He advanced the hypothesis, that the 

 distribution of the boulders which are scattered over the 

 valley of Switzerland* and on the sides of the Jura, may be 

 accounted for in this way. This opinion, which he expressed 

 in a brief treatise, was received with almost unanimous in- 

 credulity ; so generally adopted was Saussure's theory, which 

 accounted for these phenomena by the supposition that the 

 Alpine chain had formerly been broken through at various 

 points, allowing vast lakes, before shut up within its walls, 

 to escape with violence.! M. Agassiz, as we hear, was 

 among the sceptics ; and, in 1836, visited M. de Charpentier 

 with the view of persuading his friend to relinquish an hypo- 

 thesis which he considered untenable. But the latter, in- 

 stead of entering into a discussion, conducted Agassiz to the 

 places themselves on the Mer de Glace, at Chamouni, where 

 his observations had been made. He shewed him the glacier 

 actually at work in transporting boulders, and in its passage 

 polishing and rounding the rocks at its sides. A light now 

 burst upon the mind of M. Agassiz ; not only did he admit 

 that the blocks found in the valley of Switzerland might have 

 been carried thither in this manner, but he saw, moreover, 

 at a glance, the immense bearing of this fact, and the effect 

 it must necessarily have on the science of Geology. 



* The northern part of Switzerland, between the Bernese Oberland and the 

 Jura, goes by this name. 



t For some account of Saussure's theory, see LyelVs Elements of Qeology, 

 American edition, vol. i, p. 245. 



