( 104 ) 



On the Downward Progress of the Glaciers of the Alps. 

 By Ed. Collomb. 



Glaciers being the definite result of meteorological and 

 climatological phenomena, their secular encroachment upon 

 the lower valleys of the Alps may serve as a term of com- 

 parison to determine the changes that have taken place in 

 the climate of the country. 



This encroachment may take place in two ways, either 

 by the progression of their frontal portion, or by the swelling 

 out of their lateral parts. 



We may have the case of a. glacier with the frontal part 

 alone advanced forward, without the parts situate towards 

 the middle undergoing any dilatation. The reverse of this 

 may, on the other hand, present itself; that is to say, the ter- 

 minal talus may remain many years nearly stationary, and 

 yet we may observe a sensible expansion of the surface in 

 the middle region. Glaciers, therefore, exhibit two modes 

 of proceeding in encroaching upon the land, one frontal, the 

 other lateral. 



These phenomena depend on three causes which act inces- 

 santly on the physiology of glaciers, if we may use such an 

 expression. These are the alimentation, movement, and abla- 

 tion. 



The alimentation of glaciers, in other words the cause of 

 their existence, is to be found in the quantity of snow which 

 falls in the whole zone of the Alps situate above from 2800 

 to 3000 metres. At this altitude, the solar or ambient heat 

 is insufficient to melt the snow that falls in the course of the 

 year. In these high regions the alimentation exceeds the 

 melting power, and if a movement did not take place from 

 the first origin of the glaciers, at the end of a few ages such 

 an accumulation of neve would ensue in these regions, that 

 the conditions of existence in which the valleys of the Alps 

 now are, would be completely changed. 



At a height of 3000 metres, about 17 metres of snow fall 

 annually; audits primitive density, according to M. Dollfus's 

 experiments, is 85 kilogrammes* the cubic metre. By sinking, 



* Kilogramme is equal to 2 pounds i ounces avoirdupois. 



