176 Report of the Researches of M. Agassiz, 



seriously entertained or examined; and we cannot hope to 

 arrive at any positive conclusions, except by sounding the 

 glacier, or at least placing ourselves in circumstances where 

 we may continually observe it. 



Finally, the whole of the theory, whether in relation to 

 physics or geology, had to endure attacks from a variety of 

 quarters. Infiltration was strictly denied by some, and many 

 were opposed to the notion that the glacier was frozen to the 

 parts beneath ; and admitting the facts which appeared con- 

 trary to this opinion, the theory of gliding must again be can- 

 vassed. 



The phenomena of glaciers, in connection with their change 

 of position, also become the subject of various attacks. Some 

 had endeavoured to restrict their influence within very nar- 

 row limits ; and some philosophers maintained the idea, that 

 the glaciers, at no epoch, had advanced more than half a league 

 beyond their present limits. Others allowed that at one time 

 they must have reached the issues of the great valleys ; whilst 

 others prolonged their course as far as the Jura. On the 

 other hand, there were a number of geologists who adopted 

 the opinion of M. Agassiz as the most probable, and thought 

 that they had discovered erratic phenomena in many localities 

 and countries where the presence of glaciers had never before 

 been dreamt of. 



The theory of currents even, was subjected to many changes, 

 especially as regarded the origin of the pretended great 

 ones. The time was when it was with much simplicity 

 supposed that an impulsion, — some violent shock, — occurred 

 at^the summit of the Alps, and had forced from the spot, with 

 unheard-of velocity, enormous debris of rocks. It was long 

 before a cause for these currents was thought of. First, it was 

 conceived that the district of the Valais had been an immense 

 lake, whose waters had overwhelmed the plain in consequence 

 of a cataclysm which separated the Dent du Midi from the 

 Dent de Morcles. Others, again, assuming as a type the de- 

 bacle of the valley of Bagnes, fancied that many lakes were 

 formerly barred by glaciers, — ^that when these maintaining 

 barriers came to be broken, currents were produced which 



