This is no theoretical explanation; there are such
cases in Switzerland, where holes in the ice are formed immediately
above the summit of hills or prominences over which the glacier passes,
and into which it drops its burdens. Of course, where the ice is
constantly renewed over such a spot by the onward progress of the
glacier, these materials may be carried off again; but if we suppose
such a case to occur at the breaking up of the glacier-period, when the
ice was disappearing forever from such a spot, it is easy to account for
the poising of these large boulders on prominent peaks or ledges.
The appearances about the _roches moutonnees_, especially the straight
scratches and grooves on the side up which the ice ascended, have led to
a mistaken view of the mode in which large boulders are transported by
ice. It has been supposed, by those who, while they accepted the glacial
theory, were not wholly conversant with the mode of action of glaciers,
that, in passing through the bottom of a valley, for instance, the
glacier would take up large boulders, and, carrying them along with it,
would push them up such a slope and deposit them on its summit. It is
true that large boulders may sometimes be found in front of glaciers
among the materials of their terminal moraines, and may, upon any
advance of the glacier, be pushed forward by it.
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