1842.] THE HER DE GLACE AT THE END OF SUMMER. 27 



above three months during which I have studied it, are so great 

 and remarkable, and in some respects so unexpected, as to be 

 of capital importance in any theory which may be proposed. 



I was very greatly struck with the change in the general 



appearance of the glacier during my absence, from the 10th 



August to the 10th September. I left it comparatively high 



and tumid in the centre, at no great depth below the arrete of 



its natural boundary, the moraine by its side ; and fissured by 



crevasses, deep and rather narrow, with well defined vertical 



walls. On my return, the icy mass had most visibly sunk in 



its bed ; it seemed to me to have a wasted, cadaverous look ; 



the moraines protruded far higher than before from its sides, 



and the ice itself clinging to the moraine at a considerable 



height above its general level, was covered by the fallen masses 



of stone and gravel which had rolled down the inclined plane 



formed by this central subsidence. The whole resembled 



somewhat the Wye, or some of those narrow tidal rivers whose 



muddy banks are left exposed by the retreat of the ocean. 



That this subsidence was in a good measure occasioned by the 



melting of the ice in contact with the bottom of the valley in 



which it lies, and by the falling together of the parts in a soft 



and yielding state, owing to a complete infiltration of the 



whole mass with water during the warm season of the year, 



was proved by a variety of circumstances which I shall not stop 



to detail. I may mention however, that the crevasses were 



wider but less deep and regular excessively degraded on the 



side to which the mid-day sun had free access, and in many 



places where several crevasses nearly joined, the icy partitions 



had sunk gradually towards a level, and thus rendered the 



fissured parts of the glacier more easily traversed than at an 



earlier part of the season. It is plain, too, that the fact of the 



more rapid advancement of the centre of the glacier mentioned 



in my earliest letter, implies a subsidence of that part, and a 



consequent drain from the lateral ice, to supply the vacuity 



which it leaves. 



It will at once be understood that the change of which I 



