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Updated: May 8, 2025
Cold winds blow over it from the new mountains; probably vast regions of it are swept by icy blasts from the glaciated lands. As these conditions advance in the Permian period, the forests wither and shrink. Of the extraordinarily mixed vegetation which we found in the Coal-forests some few types are fitted to meet the severe conditions.
Leaving modern Vilcabamba, we crossed the flat, marshy bottom of an old glaciated valley, in which one of our mules got thoroughly mired while searching for the succulent grasses which cover the treacherous bog. Fording the Vilcabamba River, which here is only a tiny brook, we climbed out of the valley and turned westward. On the mountains above us were vestiges of several abandoned mines.
Some of them were distinctly glaciated even belong the tide-line, the effects of wave washing and general weathering being scarce appreciable as yet. Some of the larger islets had a few trees, others only grass. One looked in the distance like a two-masted ship flying before the wind under press of sail.
In what way can a wind-carved pebble be distinguished from a river-worn pebble? from a glaciated pebble? We have already seen that the ocean is the goal at which the waste of the land arrives. The mantle of rock waste, creeping down slopes, is washed to the sea by streams, together with the material which the streams have worn from their beds and that dissolved by underground waters.
In this way pebbles torn by the inland ice from the rocks of the interior of Greenland and glaciated during their carriage in the ground moraine are dropped at last among the oozes of the bottom of the North Atlantic. We are now to study the geological work of the currents of the atmosphere, and to learn how they erode, and transport and deposit waste as they sweep over the land.
The single exception was, I am convinced, one of observation and not one of fact, namely, I saw no glacial scratches on the rocks; but geologists know how rare these are on natural exposures in some districts that have certainly been glaciated, and will not be surprised that in a hurried visit of only a few hours I should not have discovered any.
But as the time which has elapsed since the disappearance of the glaciers is much less than that occupied in the formation of ordinary soil, this decay has in most cases not yet gone very far, so that in a cubic foot of glaciated waste the amount of material available for plants is often only a fraction of that held in the soils of immediate derivation.
In this way are formed the curious depressions in drift-covered regions called kettles or sinks. On these decaying glaciers we may also find many interesting lessons on the formation of boulders and boulder-beds, which in all glaciated countries exert a marked influence on scenery, health, and fruitfulness.
Thus in the valley of the Nile there are fields which have been giving rich grain harvests probably for more than four thousand years, without any other effective fertilizing than that derived from the mud of the great river. The group of glaciated soils differs in many ways from either of those mentioned.
That is one reason why glaciated New England contains over forty per cent of all the developed water-power in the United States. Far more important, however, than the glacial lakes and rivers is the fertile glacial soil. It comes fresh from the original rocks and has not yet been exhausted by hundreds of thousands of years of weathering.
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