Slowly this twelve thousand feet of strata
emerged into the sunlight. In the uplifting processes, the surface of the
earth, where they were, became tilted, and these strata therefore "dipped"
or "tilted" away from the perpendicular. As they emerged, weathering and
erosion began. It is most probable that this process of degradation began
and continued while the topmost strata were at or near sea level, so that
it was a simultaneous process with the uplift.
Erosion of the Algonkian. How many centuries this weathering and washing
away process consumed no one knows. At the close of this epoch, however,
the Algonkian strata had been eroded almost away, owing to its tilted
condition, so that in some places even the surface of the Archaean was
exposed, and suffered the planing-down process. Figure 1 on plate facing
page 98 is a suggestion as to the possible appearance of the rocks at this
time.
Even then, in those far-away, early ages of history, if one had been
present to measure these strata, he would have discovered the astounding
fact that, although he had measured them and found twelve thousand feet
before they began to emerge from the ocean, there were but about five
hundred feet of them left. This is one of the interesting facts in
geology, - that an observant reader can deduce so much from so little.
The twelve thousand feet deposit. "But," asks the layman, "I cannot
possibly see how, if only five hundred feet of strata are left, any one
could ever tell that there were once twelve thousand feet. If eleven
thousand five hundred feet are gone, how do you know they ever existed?"
A very reasonable question and one very easily answered. Refer to the
sketch. Let the bracket on the right show the present width of the
remaining strata, viz: five hundred feet. Now observe the tilted condition
of the remnants. To get the original height of the depositions begin with
No. 1, the stratum nearest the Archaean and measure that. Suppose it gives
us five hundred feet. No. 2 gives two hundred feet; No. 3, five hundred
feet; No. 4, one hundred and seventy-five; and so on up to No. 14. As these
strata were deposited horizontally, all we have to do is to mentally
replace them in their horizontal position. Throw the tilted strata back
again into their original condition, and by this method of measurement it
is seen that the twelve thousand feet can be made up. Figure 2, facing page
98.
Another interesting question here arises: "What became of the vast quantity
of sand and silt and pebbles that formed and were carried away during such
a gigantic process? For, think of it, eleven thousand five hundred feet of
strata, or rock, two miles high, almost three times as high a mass as the
present distance in vertical height from El Tovar to the river!
