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In the countless Post-Miocene ages which preceded the glacial period there was ample time for the slow erosion by water of all the principal hydrographical basins of the Alps, and the sites of all the great lakes coincide, as Professor Ramsay truly says, with these great lines of drainage.
There was something awe-inspiring in the vast antiquity of that furrowed lunar surface, by far the oldest thing that mortal eye can see, since, while observing the ceaseless political or geological changes on earth, the face of this dead satellite, on account of the absence of air and water and consequent erosion, has remained unchanged for bygone ages, as it doubtless will for many more.
In the great plains of North America two of the divisions, that is, the Atlantic coastal plain of the southeast and the peneplain of the northwest, owe their present form to the forces of erosion. The other two, that is, the prairies and the high plains, still bear the impress of the original processes of deposition and have been modified to only a slight extent by erosion.
Resolutions were adopted covering the entire subject of conservation as shown in one of them as follows: "We agree that the land should be so used that erosion and soil-wash shall cease; that there should be reclamation of arid and semi-arid regions by means of irrigation, and of swamps and overflowed regions by means of drainage; that the waters should be so conserved and used as to promote navigation, to enable the arid regions to be reclaimed by irrigation, and to develop power in the interests of the people; that the forests which regulate our rivers, support our industries, and promote the fertility and productiveness of the soil should be preserved and perpetuated; that the minerals found so abundantly beneath the surface should be so used as to prolong their utility; that the beauty, healthfulness, and habitability of our country should be preserved and increased; that the sources of national wealth exist for the benefit of the people, and that monopoly thereof should not be tolerated."
I found at the great Colorado Cañon, that the more the monuments of erosion were suggestive of human structures, or engineering and architectural works, the more I was impressed by them. We are pleased when Nature imitates man, and we are pleased when man imitates Nature, and yet we recoil from the thought that life is only applied mechanics and chemistry.
Sharp peaks, knife-edged crests, deep valleys with ungraded slopes subject to frequent landslides, are all features of Alpine scenery typical of a mountain range at this stage in its life history. They represent the survival of the hardest rocks and the strongest structures, and the destruction of the weaker in their long struggle for existence against the agents of erosion.
"He had made a discovery at the source of that little tributary, where the erosion of the glacier had opened a rich vein, and on following the stream through graywackes and slate to the first gravelled fissure, he had found the storage plant for his placer gold.
Since some of the rocks are hard and others soft and since all have been exposed to extremely long erosion, the topography of New England consists typically of irregular masses of rounded hills free from precipices. Here and there hard masses of unusually resistant rock stand up as isolated rounded heights, like Mount Katahdin in Maine.
Though rainfall increases, destructive floods become fewer, for the humus and the leaves on the ground in the forests hold the water as in a vast sponge, and, as we have seen in the preceding chapter, they keep the waters in check and distribute the rainfall gently and evenly on the lands below. They thus prevent erosion of the hillsides and balance the water supply of rivers.
The upper is more than five thousand feet thick and consists of shales and sandstones with some limestones. The lowest member is a basal conglomerate composed of pebbles derived from the erosion of the dark crumpled schists beneath, schists which are supposed to be Archean.
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