Down
Their Slopes Ran The Earliest Watercourses, First As Rills, Then As Creeks,
Finally As Rivers.
The higher the peaks ascended, the more the accompanying
land was lifted up, and therefore the longer and deeper
Became the rivers.
The course of a river once established, it is exceedingly difficult to
change it - hence the law that geologists call "the persistence of rivers."
By and by, the uplifted country appeared as one vast area of river valleys,
separated by stretches of plateau. Little by little, working by laws that
are pretty well understood, the swift flowing avers cut downwards. When
their velocity ceased, the widening of the river courses began, and
progressed with greater rapidity, so that, in time, the divides that
intervened between the rivers were worn away, - a process rudely shown in
Fig. 5 A. B. C. and D. of plate on page 110.
The Formation of the Canyon. Now, in imagination, let us hark back to the
day when this plateau was in the condition thus described. Nearly
everything in the way of strata has been planed down to the Carboniferous
rocks. The plateau is about at sea level. One great river already exists,
with two arms, now called the Green and the Grand, the main river some day
to be known as the Colorado. Slowly the uplift begins. It is a fairly even
process, and yet there is slightly more pressure brought to bear under the
southern portion, so that the whole mass has a slight tilt to the north.
Professor Salisbury found certain beds of rock at seven thousand eight
hundred feet above sea level at the base of the San Francisco Mountains
near Flagstaff.
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