Chai'pentier's Essaj/ on Glaciers^ 107 



moraines. M. de Charpentier has studied this part of the 

 subject with much care ; he has distinguished the forms 

 which these accumulations of blocks assume, according as 

 the glacier advances, remains stationary, or diminishes ; ac- 

 cording as they are formed against an escarpment, or on the 

 height of a precipice, &c. He invariably distinguishes be- 

 tween a fallen mass of rocks and a moraine, by the former 

 containing only one kind of blocks, while moraines are com- 

 posed of angular and rounded blocks, and such as are rubbed 

 by the movement of the ice, including at the same time 

 various species or varieties of the rocks entering into the con- 

 struction of the mountains which overhang the glacier. 



The phenomena belonging to superficial moraines, to their 

 pedestal of ice (which they form by preventing the fusion of 

 that part of the glacier which they cover), to the dislocation 

 and scattering they undergo when the glacier which bears 

 them enlarges or melts, are all treated in detail in M. de Char- 

 pentier' s work. He likewise particularly notices a peculiar 

 modification of moraines which he calls alluvium glaciaire. 

 This is when the debris of rocks carried by glaciers, instead 

 of falling or being heaped up on a dry deposit, fall into reser- 

 voirs of water. They then form irregularly stratified depo- 

 sits, which are distinguished from ordinary alluviums by the 

 size and shape of the blocks, and by the want of that polish 

 which characterises the pebbles of transported rocks. He 

 mentions a great many instances of this in existing glaciers, 

 and many others at the mouth of the valleys opening into the 

 great valley of the Rhone, and in localities where the glacier 

 which formed the bounding wall of the reservoir of water has 

 long since disappeared. He denominates such depositions as 

 these, the diluvium glaciaire. 



M. de Charpentier does not admit the explanation given 

 by M. Agassiz of the return to the surface of the glacier of 

 the blocks which have fallen into its interior. He conceives 

 that this result, which is otherwise well established, is solely 

 owing to the gradual melting of all the ice which covers 

 them ; but he cannot believe that there is a real rejection of 

 a foreign body by the ice, by reason of the pressure exercised 

 by the congealed water around its sides, as the distinguished 



