passes, are minute compared with, the accumulations which are furnished from other sources. These great rubbish-heaps are formed, one may say almost entirely, from débris which falls, or is washed down the flanks of mountains, or from cliffs bordering glaciers; and are composed, to a very limited extent only, of matter that is ground, rasped, or filed off by the friction of the ice.
If the contrary view were to be adopted, if it could be maintained that "glaciers, by their motion, break off masses of rock from the sides and bottoms of their valley courses, and crowd along every thing that is movable, so as to form large accumulations of débris in front, and along their sides,"[1] the conclusion could not be resisted, the greater the glacier, the greater should be the moraine.
This doctrine does not find much, favour with those who have personal knowledge of what glaciers do at the present time. From De Saussure[2] downwards it has been pointed out, time after time, that moraines are chiefly formed from débris coming from rocks or soil above the ice, not from the bed over which it passes. But amongst the writings of modern speculators upon glaciers and glacier-action in bygone times, it is not uncommon to find the notions entertained, that moraines represent the amount of excavation (such is the term employed) performed by glaciers, or at least are comprised of matter which has been excavated by glaciers; that vast moraines have necessarily been produced by vast glaciers; and that a great extension of glaciers—a glacial period—necessarily causes the production of vast moraines. It is needless to cite more
- ↑ Atlas of Physical Geography, by Augustus Petermann and the Rev. T. Milner. The italics are not in the original.
- ↑ "The stones that are found upon the upper extremities of glaciers are of the same nature as the mountains which rise above; but, as the ice carries them down into the valleys, they arrive between rocks of a totally different nature from their own."— De Saussure, § 536.
are separated by mountain ridges, or which, at least, have islands of rock protruding through the ice. The small moraines contributed by one affluent are balanced, probably, by great ones brought by another feeder.
