FORMATION OF CREVASSES. 
201 
of the transverse direction of the crevasses, or even their convexity towards the origin, 
from year to year, seems to admit of no other explanation. But besides this, I can 
affirm, from a careful observation of the crevasses of the Mer de Glace from June to 
September in one year, that the changes which they underwent were such as pre- 
clude the possibility of a crevasse of autumn being merely preserved by the snow of 
winter, and re-appearing afresh in spring as it had done the previous one. The thing 
is impossible, because the character of the crevasse is essentially altered. In order 
that an autumnal crevasse may become a spring crevasse it must be sealed up, an- 
nihilated, and opened again. A glance at the three sections in Plate X. fig. 3, 
will illustrate this. No. 1 shows crevasses freshly opened soon after the snow has 
quitted the surface of the ice — the edges are sharp, the sides vertical, the openings 
so small that they may be easily stepped across, and in other instances they are not 
wider than may admit the blade of a knife. No. 2 shows the crevasse opened to its 
widest extent by the acceleration of the motion, by the force of the sun which has 
altogether wasted away the side with the southern exposure, and by the copious 
drippings of the melting ice and mild rain. No. 3 (which as well as No. 2 is taken 
from a sketch on the spot, No. 1 being done from recollection) shows what I have 
elsewhere called the state of collapse of the glacier, which affords the most direct pos- 
sible evidence of its plastic condition ; for we there see, not merely the prominences 
worn away and blunted by the heat of summer, but subsiding into the hollows, the 
crevasses being choked by the yielding of their sides, and the glacier again resumes 
a traversable character, only that the plane surface of spring is changed into irregular 
undulations preparatory to a complete amalgamation of the whole glacier into one 
mass*. 
The collapse is thus described in my Journal of 1842, written at the time, and there- 
fore more emphatic and unbiassed than after my theoretical views had been matured 
and published. “ 1842, Sept. 16, Friday. The level [of the Mer de Glace at the ‘angle’] 
has sunk since the 9th of August, nine feet 8^ inches. The effect of this immense 
fall is abundantly evident in this part of the glacier. On my first visit this time [*’. e. 
after an absence of a month], on the 10th, I was quite struck with its shrunk appear- 
ance, as I was today with the collapsed state of the crevasses. There cannot be a 
question but that the glacier has subsided bodily into its bed, and that the semifused 
pliancy of its materials causes them to recover a uniform and lower level. The cre- 
vasses are much less deep than in July and August, as at that time they were larger 
and more numerous than in June. They are collapsed and (opposite Trelaporte) 
almost soldered up ; the edges all rounded and melted by the sun’s heat.” The phe- 
nomena here described, “the shrunk appearance,” “the semifused pliancy," “the 
soldered crevasses,” “ the rounded edges,” convey to the attentive spectator an intui- 
tive conviction of the plasticity of ice at the thawing season, which no words can 
* See Travels, p. 174 ; and Fourth Letter on Glaciers. 
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