Let Us, Therefore, Take A Seat At El Tovar, And Try To Read A
Few Pages Of The Stone Book Of Creation As Opened There.
Suppose all this
vast region at about sea level, and the uplift just beginning.
The course
of the Colorado River is already well defined. As the uplift continues, the
cherty limestone and possibly the cross-bedded sandstone are both cut
through, as the plateau slowly emerges. Whether the process of uplift is
slow or rapid, as soon as a stratum emerges, it becomes subject to the
influences of weathering, and the uppermost strata appearing first, they
are weathered most. Hence the recession of the uppermost cliffs is greater
than that of the cliffs lower down. The differences in hardness and
resistance to weathering are alone responsible for the step-like profile of
cliffs and terraces. The lower platform owes its width entirely to the
rapid weathering and recession of the soft shales, which overlie the Tonto
sandstones. The red-wall limestone, on the other hand, remains standing out
as a cliff because of its exceeding durability.
The Faults. During the final uplift, the river cut through the Cambrian and
Algonkian strata, and into the Granite Gorge as we find it to-day, and the
process is still slowly going on. During these various periods of uplift,
there were other changes occurring. Sometimes the uplift was uneven,
certain parts of the plateau being lifted more rapidly than other parts;
then occurred breaks in the strata, called faults.
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