M. Agassiz 07i Glaciers, Moraines, and Erratic BlocJcs. 371 



it. It follows, therefore, that it is onl}' the movement of great 

 masses of ice immediately upon solid masses, which can pro- 

 duce effects similar to the polish which we remai-k upon the 

 margins of the retreating glaciers. This last phenomenon per- 

 fectly resembles that which is exhibited by the laves of the 

 Jura. 



By this similarity alone we might be led, in application to 

 this phenomenon, to conclude, that like causes have produced 

 like effects. But there is another class of considerations which 

 more directly lead us to associate these two phenomena, and 

 which will compel even those who would resort to different 

 agencies, to regard them under one and the same point of view, 

 AVe have witnessed moraines on the very margin of the lake 

 of Geneva, and on both banks, at the same elevation ; we have 

 thereby the certainty that there was a time when the lake was 

 frozen to the bottom, and when this ice was elevated to a con- 

 siderable height above its present level. 



But we also know that all the moraines "which remain in situ 

 are such as the glaciers leave in retiring. Since the epoch, 

 then, which I have just mentioned, or in which the glaciers 

 still debouched in the lower Swiss valleys, they have gone on 

 diminishing and retiring into the more elevated and higher 

 valleys. 



Here, then, a question naturally suggests itself, Have those 

 glaciers which have extended to the greatest distances, descend- 

 ed from the summit of the Alps ? or was there a time when the 

 ice was naturally formed beyond the limits within which we 

 now see it confined, reaching even to the Jura, and possibly 

 beyond it ? 



The level of the moraines on the shores of the liake of Ge- 

 neva, viz. 2500 feet above the sea, and the nature of the po- 

 lished surfaces on the Jura, would lead to this conclusion. We 

 have, moreover, only to mark on a chart of the levels the 

 heights of the moraines which debouch in the different localities 

 of the alpine chains, to be convinced that ice at one time 

 covered the whole of the plain of Switzerland, and reached the 

 slope of the Jura. * 



• M. Roil. Blanchet, who has been engaged upon this subject, Las some 



