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Updated: June 19, 2025


Take off from this six thousand five hundred feet, say one thousand five hundred feet, for the level of the country at the base of these two mountains, and then imagine a region five times as high as both of them, covering an area of country of possibly thirteen thousand to fifteen thousand square miles, slowly planed off by the erosive forces of nature. Formation of River Beds. How was it done?

EROSION OF TERTIARY MOUNTAINS AND PLATEAUS. The mountains and plateaus built at various times during the Tertiary and at its commencement have been profoundly carved by erosive agents. The Sierra Nevada Mountains have been dissected on the western slope by such canyons as those of King's River and the Yosemite.

The inertia of such a rock-ribbed shell is terrible, and while sometimes the erosive power of agitation and discussion suffices to weaken and destroy it, more often the volcanic fires of social convulsion are alone strong enough. The first such shock came from within the English-speaking world itself, but not in Europe.

In one case, as in the other, we observe normal deformations of a shrinking globe shielded from the erosive action of rain, which tends, on the contrary, in all the abundantly watered parts of the earth to make the concave surfaces predominate. The explanation of this structure, such as is admitted at present by geologists, seems to us equally valid for the moon."

We may infer from this instance how slight is the erosive power of clear water on hard rock. The deeps do not exceed that at the foot of the Horseshoe Falls at the present time. When the gorge was being cut along the shallows, how did the Falls compare in excavating power, in force, and volume with the Niagara of to-day? How did the rate of recession at those times compare with the present rate?

THE GREAT LAKES. The basins of the Great Lakes are broad preglacial river valleys, warped by movements of the crust still in progress, enlarged by the erosive action of lobes of the continental ice sheets, and blockaded by their drift.

What Powell calls the "recession of cliffs" comes into play. The erosive and corrasive power of water being the chief land sculptors, it is evident that there will be a continual wearing down of the faces of the bounding cliffs. The softer beds will be cut away faster than the harder, and where these underlie the harder the latter will be undermined and fall.

The forests have been cleared away, the land has been overgrazed, cultivated and exposed to the erosive attacks of sunlight, air, water and frost. Wood from the forests has been hauled to the cities and burned, has been used to construct palaces and temples, houses and ships, with no recognition of the principles of priority or renewal. If wood was available where must it go?

If after studying the erosive phenomena exhibited in the structure of the earth the student takes up the study of the accumulations of strata, and endeavours to determine the time required for the laying down of the sediments, he finds similar evidence of the earth's great antiquity.

The coral polyp seems to be doing only desultory work, and that mostly on the northeast or Atlantic side of the islands; everywhere else it has abandoned the field to the erosive action of the waves. Columbus said that Guanahani had abundance of water and a very large lagoon in the middle of it. He used the word laguna lagoon, not lago lake.

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