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Updated: June 19, 2025
Even when gathered into definite channels, ground water does not have the erosive power of surface streams, since it carries with it little or no rock waste.
It is impossible to deny that the mere geographical distribution of lakes points to the intimate connection of their origin with the abundance of ice during a former excess of cold, but how far the erosive action of moving ice has been the sole or even the principal cause of lake-basins, is a question still open to discussion.
If it has taken this length of time for the Niagara Falls to make their way back a distance of seven miles by the erosive power of the water acting on a soft shale rock supporting a stratum of limestone, the immensity of time involved by assuming that the Grand River cañon was formed in the same way is so great that the mind falters in contemplating it, especially when it is recognized that the escarpment of the Labrador Falls is of hard gneissic rock.
Beginning to develop in mountain regions, or near the poles on the lowlands, these sheets, as soon as they attained the thickness where the ice at their bottom became molten, would rapidly advance for great distances until they attained districts where the melting exceeded the supply of frozen material. In this excursion only the marginal portion of the glacier would do erosive work.
We marvel and admire as we gaze upon them now; we do more, we have to speculate as to how it was all done by the blind, unintelligent forces. Giant stairways, enormous alcoves, dizzy, highly wrought balustrades, massive vertical walls standing four-square like huge foundations how did all the unguided erosive forces do it?
The short, comparatively swift-flowing Hoffman Glacier, whose fountains extend along the south slopes of the Hoffman Range, offered a striking contrast to the one just described. The erosive energy of the latter was diffused over a wide field of sunken, boulder-like domes and ridges.
Wright has established with some approach to certainty that glacial conditions ceased in Canada and the United States about ten or twelve thousand years ago. The erosive action of the Falls of Niagara qualifies them to serve as a clepsydra, or water-clock on a grand scale; and their chronological indications have been amply corroborated elsewhere and otherwise on the same continent.
As lake deposits are normally formed in basins above the level of the sea, and as the drainage channels of the basins are always cutting down, the effect is to leave such strata at a considerable height above the sea level, where the erosive agents may readily attack them.
Clouds of dust are raised from the street and driven along by the gale. Here the roadway is swept bare; and there, in sheltered places, the dust settles in little windrows. The erosive power of waste-laden currents of air is suggested as the sharp grains of flying sand sting one's face or clatter against the window.
The Lima, however, in a large proportion of its course, has the erosive character of a torrent, for the amount of sediment which it carries down, even when it is only moderately swollen by rains, surpasses almost everything of the kind which I have observed, under analogous circumstances, in Italy.
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