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Admitting that the sharper declivity of the Kanab would enhance its power of corrasion, nevertheless we should expect to see it approach the Grand Canyon by leaps and bounds, like the Havasupai farther down, but, on the contrary, there are parts that appear to be at a standstill in corrasion, or even filling up, and its floor is a regular descent, except for the last three or four miles where the canyon is clogged by huge rocks that seem to have fallen from above.

EROSION is this power which carves away the cliffs, and CORRASION the one which saws at the bottom, the latter term, in geological nomenclature, meaning the cutting power of running water.* This cutting power varies according to the declivity and the amount of sediment carried in suspension.

It seems possible that there may have been in this region some great lake which lifted the waters up to the top of the ridge to begin their work of corrasion. Such lakes did exist; but lack of space forbids the further pursuit of this discussion here. * The character of the Grand River is similar to that of the Green, but the canyons above the mouth of the Dolores are not so long nor so deep.

* In connection with the subject of erosion and corrasion the reader is advised to study the following works, which are the standards: The Exploration of the Colorado of the West, and the Geology of the Uinta Mountains, by J. W. Powell; The Henry Mountains, by G. K. Gilbert; The Geology of the High Plateaus of Utah, and The Tertiary History of the Grand Canyon District, by C. E. Dutton.

Another is formed elsewhere, and another, and so on till all drainage is through these tributaries and away from the brink, by more or less circuitous channels to the main stream. This backward drainage leaves the immediate brink, or "rim," till the last, in its work of erosion and corrasion, and the rim consequently is left higher than the region away from it.

That is why we have canyons. The powers of erosion are far slower than those of corrasion, especially in an arid region, because they are intermittent. Where rocks take a polish, as in Marble Canyon, the scouring and polishing work of corrasion is seen in the shining bright surface as far as the water rises. This all belongs to the romance of the Water-gods, those marvellous land sculptors.

It is also clear that if, by some chance, the precipitation of the high sources should increase, the corrasion of the stream-beds in the canyons would likewise increase and outrun with still greater ease the erosion of their immediate surroundings.

The Rio Grande Dam involving the construction of a storage dam opposite Eagle, New Mexico, across the Rio Grande River will irrigate one hundred and eighty thousand acres of land in New Mexico, Texas, and Mexico. Nowhere else on the face of the globe is one so vividly impressed by the vastness of the work of corrasion as in the northwestern part of Arizona.

It is a singular fact that some side canyons, the Kanab, for example, while now possessing no running water, or at best a puny rivulet, and depending for their corrasion on intermittent floods, meet on equal terms the great Colorado, the giant that never for a second ceases its ferocious attack.

This stream we have to cross from time to time, and we find the quicksands treacherous and our horses floundering in the trembling masses. These broad canyons, or canyon valleys, are carved by the streams in obedience to an interesting law of corrasion.