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On the surface of the ice along the marginal zone, rivulets no doubt flowed in summer, and found their way through crevasses to the interior of the glacier or to the ground. Subglacial streams, like those of the Malaspina glacier, issued from tunnels in the ice, and water ran along the melting ice front as it is seen to do about the glacier tongues of Greenland.
Such subglacial rivers appear to have been formed along the margins of all the great glaciers. We can sometimes trace their course by the excavation which they have made, but more commonly by the long ridges of stratified sand and gravel which were packed into the caverns excavated by these subglacial rivers, which are known to glacialists as eskers, or as serpent kames.
Where the waters of the subglacial stream have swept the bed rock clean of débris its surface is scored, grooved, and here and there polished in a manner which is accomplished only by ice action, though some likeness to it is afforded where stones have been swept over for ages by blowing sand.
In this work the freezing and thawing of subglacial waters in any cracks and crevices of the rock no doubt play an important part. Plucking occurs especially where the bed rock is weak because of close jointing. The product of plucking is bowlders, while the product of abrasion is fine rock flour and sand.
The glacier here is practically stagnant, and lakes a few hundred yards across, which could not exist were the ice in motion and broken with crevasses, gather on their beds sorted waste from the moraine. The streams which drain the glacier have cut their courses in englacial and subglacial tunnels; none flow for any distance on the surface.
We soon left the path and took to the ice; and after wandering amongst the crevices UN PEU, to admire the wonders of these deep blue caverns, and hear the rushing of waters through their subglacial channels, we struck out a course toward L'AUTRE CÔTE and crossed the glacier successfully, a little above the cave from which the infant Rhone takes its first bound from under the grand precipice of ice.
As a contrast to all that is pure and chaste in the scene before us, there rushes out from the eastern end of the glacier a subglacial stream of thick, dirty water, much resembling, as it boils up from its cavernous outlet, the mud geyser of the Yellowstone.
In the summer time this subglacial stream is swollen by the surface waters descending through the crevices and the moulins which come from them, so that the outflow often forms a considerable river, and thus excavates in the ice a large or at least a long cavern, the base of which is the bed rock.
This action is particularly interesting, for the reason that in regions whence glaciers have disappeared the deposits formed in the old ice arches often afford singularly perfect moulds of those caverns which were produced by the ancient subglacial streams. These moulds are termed eskers.
We soon left the path and took to the ice; and after wandering amongst the crevices UN PEU, to admire the wonders of these deep blue caverns, and hear the rushing of waters through their subglacial channels, we struck out a course toward L'AUTRE CÔTE and crossed the glacier successfully, a little above the cave from which the infant Rhone takes its first bound from under the grand precipice of ice.
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