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It is plain that a stream having great declivity will be able to carry more sediment than one having little, and in a barren country would always be highly charged with sand, which would cut and scour the bed of the channel like a grindstone. As Dutton says, a river cuts, however, only its own width, the rest of a canyon being the "work of the forces of erosion, the wind, frost, and rain."
He divides its affections into apostema, ulcus, putredo sive corrosio, et casus. Apostema was abscess, ulcus any rather deep erosion, putredo a gangrenous condition, and casus the fall of the uvula. This is the notorious falling of the soft palate which has always been in popular medical literature at least.
It is its immense width, sharply defined by precipitous walls plunging suddenly down from a flat plain, declaring in terms instantly apprehended that the vast gulf is a gash in the once unbroken plateau, made by slow, orderly erosion and removal of huge beds of rocks.
An erosion surface which thus parts older from younger strata is known as an UNCONFORMITY, and the strata above it are said to be UNCONFORMABLE with the rocks below, or to rest unconformably upon them. An unconformity thus records movements of the crust and a consequent break in the deposition of the strata.
I wished to look into the great, deep, green amphitheatre which seems to lie at the head, but had glimpses of it only from a distance. How many millenniums will it be, I said to myself, before erosion will have completed its work here, and these thin, high mountain-walls will be in ruins? Surely not many. We returned to the hospitable home we had left, and passed the midday there.
There has been, however, a considerable amount of erosion on the hills, and if, as seems likely, the water-works have been out of order for several centuries, it is not surprising that all traces of them have disappeared in places. I regret very much that circumstances over which I had no control prevented my making a thorough study of the possibilities of such a theory.
There are those well meaning theorists who harp on the inherent right of every free born American to do with his land what he wants to cultivate it well or badly; to conserve his timber by cutting only the annual increment thereof or to strip it clean, let fire burn the slash, and erosion complete the ruin; to raise only one crop and if that crop fails, to look for food and support from his neighbors or his government.
The work of erosion has been very slow, as the basalt is tough and hard, and one column after another must have been undermined and reduced to pebbles, and then to sand. The Puy de Come and its lava-current, near Clermont, may be mentioned as another minor volcano of about the same age.
Its southern section, that of Mont Dore, the Cantal, and the Haute Loire, is characterised by magnificent valleys, traversing plateaux of volcanic lava, and exhibiting the results of river erosion on a grand scale; while its northern section, that of the Puy de Dôme, presents to us a varied succession of volcanic crater-cones and domes, with their extruded lava-streams, almost as fresh and unchanged in form as if they had only yesterday become extinct.
The more ornate and sculptured of the buttes is Vishnu Temple, a solid mountain of rock carved into a majestic form by centuries of erosion. Wherever one stands, at the eastern end of the Canyon, whether on the north or the south, on the promontories at the rim or on the plateaus beneath, it is the dominating and eye-compelling object.
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