106 Cliarpentiei''s JUssaj/ on Glaciers, 



the annual snows are not completely melted, — never in the 

 glaciers properly so called. 



With regard to the descending progress of glaciers, M. de 

 Charpentier ascribes it to the effect of the dilatation of the 

 water congealed, during the nights of summer, in the interior 

 of the glacier, and which tends to push the mass in the di- 

 rection which presents least resistance, that is to say, in the 

 direction of its length. This effect, which is of such a na- 

 ture as to be continually renewed, would cause an unlimited 

 increase in the glacier, if, after its arrival in the lowest val- 

 leys, the glacier were not exposed to a higher temperature, 

 which destroys it by fusion. According as the expansion and 

 the fusion counterbalance each other, or the one gains an in- 

 fluence over the other, the glacier remains' stationary, ad- 

 vances or diminishes. M. de Charpentier endeavours to 

 establish this as the true theory of the movement of glaciers, 

 on the grounds, 1st, That the motion never takes place except 

 in summer, the season of the alternate melting and congela- 

 tion of the water in the day and night, and that the glaciers 

 are stationary during winter ; 2</, That the glaciers always 

 advance, when a cold and rainy summer succeeds a winter in 

 which there has been much snow, as was the case from 1812 

 to 1818, and that they diminish when the summers are dry 

 and warm, and the snow not in great abundance, as from 

 1821 to 1826 ; Sd and lastly, That the small inclination of 

 many glaciers, and their stationary condition during winter, 

 prevents us ascribing their motion to the pressure of the snow 

 in their upper portion, as Saussure supposed. 



This expansion of the ice produces an enormous pressure 

 on the rocks which form the bed of the glacier. The fric- 

 tion resulting from the movement of the mass, aided by the 

 sand or gravel occurring between it and the rock, hollows, 

 ruts, or polishes the latter, according as the minerals consti- 

 tuting the rock are of a more or less hard or resisting na- 

 ture. The fine striae formed in this case always follow the 

 direction of the glacier's progress, — a direction which is de- 

 termined by the configuration of the ground. 



From a desire to avoid all useless repetition, we do not 

 again refer to the definitions and the mode of formation of 



