PRESSURE OF GLACIERS. )_G'# 



decrease as it progresses downwards. According 

 to the estimations of Agassiz the thickness of the 

 ice-mass in the upper parts of the greater Alpine 

 glaciers, amounts to at least 1000 feet, and in 

 some of them is, even at their lower end, nearly 200 

 feet. Hence arises the enormous thrusting power 

 of the glacier-ice, even when the slope of the 

 valley-bottom is gentle. For instance, in the case 

 of the Mer de Glace, above the vale of Chamouni, 

 Charpextier finds the inclination of the bottom 

 to be from 5° to 6° ; the fall would thus amount 

 to about one foot in ten of length. Now, it is 

 known that the pressure is proportional to the 

 steepness of the slope, and it therefore amounts, in 

 the glacier here spoken of, to one-tenth of the 

 weight of the mass of ice. Since the Mer de 

 Glace is about 5400 feet broad, this will give 

 (taking the mean thickness of the ice at only 200 

 feet), for every 100 feet of the length of the glacier, 

 the immense pressure of 6,500,000 hundred 

 weight, upon all that opposes the onward gliding 

 of the glacier mass. 



The notion which has long been rooted among 

 the inhabitants of the Alpine districts, of the 

 descent of the glacier by its own weight, has, since 

 Saussure's careful study of these remarkable 

 phenomena, also obtained the repeated assent of 

 naturalists. 



The lower surface of the glacier, that rests on the 



M 2 



