Page:Whymper - Scrambles amongst the Alps.djvu/293

Rh (through many centuries) extreme variations of temperature, the period during which such effects were produced must have widely exceeded in duration the 'glacial period' of Europe. If moraines were built from matter excavated by glaciers, the moraines of Greenland should be the greatest in the world!

The absence of moraines upon and at the termination of this great Mer de Glace is due to the want of rocks rising above the ice. On two occasions, in 1867, I saw, at a glance, at least 600 square miles of it, from the summits of small mountains on its outskirts. Not a single peak or ridge was to be seen rising above, nor a single rock reposing upon the ice. The country was completely covered up by glacier; all was ice, as far as the eye could see.

There is evidence, then, that considerable areas of exposed rock surface are essential to the production of large moraines, and that glacial periods do not necessarily produce vast moraines. That moraines are not built up of matter which is excavated by glaciers, but simply illustrate the powers of glaciers for transportation and arrangement.