372 M. Agassiz on Glaciers, Moraines, and Erratic Blocks. 



In truth, the difference of level between the elevation of the 

 moraines on the border of the lake of Geneva, of those in the 

 neighbourhood of Vevey, and on the side of Savoy, and that 

 of the polished surfaces which are observed above the margin 

 of the lake of Neuchatel, and onwards to the very summit of 

 Chaumont, is such that the sheet of ice which filled the space 

 comprised within these limits, must have had a certain inclina- 

 tion, since the level of the lake of Neuchatel is only 1344 feet 

 above the level of the sea, that of the zone of Pierre-a-Bot, 

 along which the greatest number of boulders is found, is 2150 

 feet, and the summit of Chaumont itself is only 3619 feet 

 fibove the level of the sea. 



This being the case then, we are not only entitled to attri- 

 bute to the action of ice all the polished surfaces we find on the 

 slope of the Jura, but also to regard these surfaces as a certain 

 index of the wider limits which the ice had at a former period 

 both over the Jura and the Alps. 



M. Charpentier imagines, that these masses of ice were gla- 

 ciers which were formed on the summit of the Alps, and which 

 had descended into the plain, and had then been elevated to the 

 heights in which we now find their traces, forcing before them 

 the blocks which are now reposing on the Jura. There is a 

 striking fact, however, which is in opposition to this explanation : 

 it is, that the Jura blocks are usually less rounded and even of 

 a larger size than those which ai*e found in the moraines at the 

 margin of the existing glaciers.* If our blocks had been thus 

 rolled in front of a glacier from the Alps as far as the Jura, 



time ago remarked, that the summit of the Pelerin, the mountain which over- 

 hangs Vevey, fronting the opening into the Vallais,and elevated 3301 French 

 feet above the sea, and which is composed of a coarse-grained conglomerate, 

 is polished near the top, at a spot where there is no water even to form a little 

 rivulet, and no path, or any other polishing cause which can be adduced. It 

 is therefore to a height of 3300 feet at least, that we may carry the elevation 

 of that ice which filled the basin of the Lake of Geneva, the surface of which 

 lake is now at an elevation of 1145 feet. On the summit of the Pelerin is 

 t}ie resting-place of the ice whose level was 3300 feet above the level of the 

 sea. We have no data, however, to indicate what was its thickness at this 

 place. 



* These facts do not at all agree with what M. Elie de Beaumont has de- 

 scribed respecting the valley of the Durance. 



