Observations on Glaciers. 3 



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 

 speak in the external figure of the ice, its crevasses and ine- 

 qualities, is an eifect due to the season, and must be repeated 

 every year. Were the summer considerably prolonged, the 

 annihilation of the glacier would take place from a simple con- 

 tinuation of the process, namely, the increased velocity of the 

 central part, the exaggeration of the crevasses in width, and 

 the falling of their walls, or rather the gradual subsidence of 

 the elevations, softened by the warmth, into the hollows which 

 separate them, whilst the moraine would be left in all its 

 continuity as a witness of the original boundary of the glacier. 

 The ice must possess within itself some reproductive power 

 (if the phrase may be permitted,) to restore it in spi'ing to the 

 level from whence it had descended ; and since crevasses thus 

 form, extend, and again vanish, — perhaps in a single season 

 but certainly in a very few years, — we must consider the glacier 

 as a much more plastic body than it has commonly been ima- 

 gined. 



I state it, then, as a result of observation the most direct, 

 that, in the early part of summer, the glacier level is highest, 

 and the fissures least numerous. The latter form and widen 

 especially during the months of June and July ; and, in the 

 beginning of August, the glacier is most difiicult to traverse, 

 (generally speaking), owing to the multitude and sharpness of 

 these cracks ; but later, the prolonged sunshine and autumnal 

 rains, not only reduce the ice to water, and thus carry ofi^ a part 

 of its surface, but leave the remainder in a softened and plastic 

 state, in which the tendency is to a general subsidence of all 

 the elevations, whilst the prolonged excess of velocity of the 

 central above the lateral parts, causes an increased hoUow- 

 ness and subsidence there, and produces a great Assuring, the 

 latei'al ice still clinging to the moi'aines, which it is compelled 

 gradually to uncover. Before spring, by some process which 

 it remains to explain, the level of the ice is restored (supposing 

 the glacier not to be permanently wasting). 



