The Glaciers of the Alps: Being a narrative of excursions and ascents, an account of the origin and phenomena of glaciers and an exposition of the physical principles to which they are relatedTyndall, John
Science
The Glaciers of the Alps: Being a narrative of excursions and ascents, an account of the origin and phenomena of glaciers and an exposition of the physical principles to which they are related
Tyndall, John
Alps -- Description and travel; Glaciers -- Alps
Near the side of the Glacier du Geant, above the promontory of
Trelaporte, the ice is rent in a remarkable manner. Looking upwards from
the lower portions of the glacier, a series of vertical walls, rising
apparently one above the other, face the observer. I clambered up among
these singular terraces, and now recognise, both from my sketch and
memory, that their peculiar forms are due to the same action as that
which has given their shape to the "billows" of the Mer de Glace. A
series of profound crevasses is first formed. The Glacier du Geant
deviates 14 deg. from the meridian line, and hence the sun shines nearly
down it during the middle portion of each day. The backs of the ridges
between the crevasses are thus rounded off, one boundary of each fissure
is destroyed, or at least becomes a mere steep declivity, while the
other boundary being shaded from the sun preserves its verticality; and
thus a very curious series of precipices is formed.
Through all this dislocation, the little moraine on which I have placed
the letter _b_ in the sketch maintains its right to existence, and under
it the laminated structure of this portion of the glacier appears to
reach its most perfect development. The moraine was generally a mere
dirt track, but one or two immense blocks of granite were perched upon
it. I examined the ice underneath one of these, being desirous of seeing
whether the pressure resulting from its enormous weight would produce a
veining, but the result was not satisfactory. Veins were certainly to be
seen in directions different from the normal ones, but whether they were
due to the bending of the latter, or were directly owing to the pressure
of the block, I could not say. The sides of a stream which had cut a
deep gorge in the clean ice of the Glacier du Geant afforded a fine
opportunity of observing the structure. It was very remarkable--highly
significant indeed in a theoretic point of view. Two long and
remarkably deep blue veins traversed the bottom of the stream, and
bending upwards at a place where the rivulet curved, drew themselves
like a pair of parallel lines upon the clean white ice. But the general
structure was of a totally different character; it did not consist of
long bars, but approximated to the lenticular form, and was, moreover,
of a washy paleness, which scarcely exceeded in depth of colouring the
whitish ice around.
[Sidenote: GROOVES ON THE SURFACE. 1857.]
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