But when the glacier has been washed clean by rain, and the light
strikes upon it in the right direction, these lines become perfectly
distinct, where, under different conditions, they could not be discerned
at all. After passing many summers on the same glacier, renewing my
observations year after year over the same localities, I can confidently
state that not only do the lines of stratification exist throughout the
great glacier of the Aar, but in all its tributaries also. Of course,
they are greatly modified in the lower part of the glacier by the
intimate fusion of its tributaries, and by the circumstance that their
movement, primarily independent, is merged in the movement of the main
glacier embracing them all. We have seen that not only does the centre
of a glacier move more rapidly than its sides, but that the deeper mass
of the glacier also moves at a different rate from its more superficial
portion. My own observations (for the details of which I would again
refer the reader to my "Systeme Glaciaire ") show that in the higher
part of the glacier, especially in the region of the _neve_, the bottom
of the mass seems to move more rapidly than the surface, while lower
down, toward the terminus of the glacier, the surface, on the contrary,
moves faster than the bottom.
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