228 



HELMHOLTZ 



(11,000 feet above the sea), and down the Italian side to the 

 valley of Aosta. 



The surface of the Mer de Glace shows four of the rocky 

 walls which we have designated as medial moraines. The 



first, nearest the side of the glacier, is formed where 

 the two arms of the Glacier du Talefre unite at the lower 

 end of the Jardin; the second proceeds from the union of 

 the glacier in question with the Glacier de Lechaud; the 

 third, from the union of the last with the Glacier du Geant; 

 and the fourth, finally, from the top of the rock-ledge 

 which stretches from the Aiguille du Geant towards the 

 cascade (g) of the Glacier du Geant. 



To give you an idea of the slope and the fall of the glacier, 

 I have given in FIG. 106 a longitudinal section of it accord- 



