laS M. Ch. Martins on the 



composed of the two glaciers united. Tlius, at the junction 

 of the Arve and Rhone, we see the turbulent water of the. 

 torrent mingled at the central point of confluence with the 

 transparent waters of the river purified by its passage across 

 the lake of Geneva. The median moraine partakes of the 

 motion of the medium part of the glacier ; after a longer or 

 shorter transit, each block reaches in its turn the terminal 

 escarpment, rolled along the declivity till it be stopped at 

 this rampart of ice. On the glacier of the Aar, the length of 

 which is 8 kilometres, a block takes 133 years to traverse the 

 space comprised between the promontory of Abschwung, 

 which separates the two principal affluents and the lower 

 extremity. The accumulation of these blocks forms a con- 

 centric mound at this extremity ; this is the terminal or 

 frontal moraine, which differs from all of which we have 

 spoken in this, that it does not rest upon the glacier, but be- 

 fore it, on the bottom of the valley. 



We are now acquainted with three kinds of moraines; 

 some superficial^ extended on the surface of the glacier, and 

 which are divided into lateral and median moraines, accord- 

 ing as they are on its sides or in the middle ; and the ter- 

 minal moraine, produced by the accumulation of blocks which 

 form the terminal escarpment of the glacier, and rest upon 

 the ground. There is still another kind of moraine, that is, 

 the layer of sand and pebbles interposed between the lower 

 surface of the glacier and the subjacent rock. I shall desig- 

 nate this deep moraine {moraine profonde) in order to distin- 

 guish it from such as are superficial and terminal. 



4. Pebbles Striated by existing Glaciers. 



Carried slowly along on the surface of a glacier, all the 

 blocks of superficial and terminal moraines retain their ori- 

 ginal forms. The edges of these blocks are sharp, the angles 

 acute, as at the moment when they fell upon the ice. They 

 present no marks of wear or friction, such as we notice on 

 stones rolled and rounded by the action of water. We may 

 detach from theni beautiful groups of crystals, as perfect as 

 when in their original bed ; for, except the first fall which 

 precipitated them on the glacier, these masses have been sub- 



