234 



to explain the origin of a glaciet For as the ice is being 

 constantly diminished at the lower end by melting, it would 



FIG 



ntirely disappear if fresh ice did not continually press 

 'forward from above, which, again,- is made up by the 

 snowfalls on the mountain tops. 



But by careful ocular observation we may convince our- 

 selves that the glacier does actually move. For the inhab- 

 itants of the valleys, who have the glaciers constantly 

 before their eyes, often cross them, and in so doing make 

 use of flie larger blocks of stone as sign posts detect this 

 motion by the fact that their guide posts gradually descend 

 in the course of each year. And as the yearly displacement 

 of the lower half of the Mer de Glace at Chamouni amounts 

 to no less than from 400 to 600 feet, you can readily con- 



