第40章 CHAPTER XIII(3)

Absence of Certain Strata. To shorten our story, let me at once say that during the periods that the Ordovician, the Silurian and the Devonian were forming, the Grand Canyon region was either above water so that it received none of these sediments, or, if any were deposited, they were almost entirely removed by the weathering processes before described, ere the region again sank into the ocean to receive the deposits of the Carboniferous epoch.

The Carboniferous. During this latter period, more than three thousand feet of strata were deposited. These are the most striking in appearance of all the Canyon strata, for they reach from the Tonto shales to the rim, and consist of three principal strata (with many smaller ones in between). The largest is the red-wall limestone, which constitutes the base of nearly all the architectural forms found in the Canyon, and is the thickest of all the strata. It presents the "tallest" wall of the series. The two separate walls, one above the other, on the top of the Canyon, as seen in the arms of the amphitheatre at El Tovar, are the other two wide members of this Carboniferous period. The lower is the cross-bedded sandstone, and the upper the cherty limestone. There is a remarkable difference in the appearance and the material of which these Carboniferous strata are formed, and those of the East and Europe. We generally think of coal-beds--carbon when this period is mentioned. Here there are none. In the East, in England, and in other parts of Europe, vast marshes existed in this period, and the rank vegetation of these marshy areas formed the coal-beds, with which the Carboniferous there abounds. It is only by the fossils found that the periods to which the various strata belong are determined, and the fossils, millions of which abound in the upper limestone, are clearly of the Carboniferous epoch.

As these strata and this period bring us to the "rim" of the Canyon, it might be easy to imagine that the processes of uplift and subsidence, and deposition of more strata, as far as the Canyon region is concerned, now cease. Such, however, is not the case.

Later Strata. As we go away from the Canyon, either north or east, we find thousands of feet more of the later depositions, and the geologists affirm that many of these at one time may have overlaid the Canyon region. There is circumstantial evidence, amounting almost to proof, and Figure 3 of plate facing page 99 suggests what that evidence is. It should be carefully noted that the Canyon has been cut through the highest portions of a ridge, which runs generally from east to west, and the slopes of which, therefore;were north and south from the ridge. As one travels north from the Canyon, he finds all the way along, for hundreds of miles, that he goes on a down slope for a number of miles and then suddenly comes to the jutting edges of slightly tilted strata (only 2 degrees) which make a cliff up which he must climb. Arrived at the top of this, the downward descent begins again, until another ridge of these slightly tilted strata appears, see Figure 3 of plate facing page 99. Thus he continues up into Utah, and south and east into Arizona.

Now, in imagination, restore these cliffs of Permian, Triassic, Jurassic and even Cretaceous strata over the whole Canyon platform. Figure 4 of plate facing page 99.

Red Butte, which is the prominent landmark seen from the railway on the right, when going from Williams to the Canyon, is said to be a remnant of the Permian.

Deposition of Strata in Shallow Water. It is, I believe, generally accepted by the geologists that the accumulation of much of the sediments of the Cambrian, Carboniferous, Permian, Triassic, Jurassic and Cretaceous periods took place in shallow water, and that the sea bottom slowly sank under the weight of the increasing deposits. Hundreds, thousands of years must have elapsed during the process, for the indications are that the sinking did not exceed a few inches every hundred years! As carefully measured, these sediments then amounted to about two miles. Imagine, then, these Cambrian rocks, that at El Tovar are clearly seen above the "granite" or Archaean, sunk in the ocean, to the depth of two miles, and covered over with the various strata, the topmost of which was barely above sea level at periods of low tide.

Cretaceous Uplift. Then began another epoch of uplift. Slowly the Cretaceous rocks emerged from the sea, and were subject to the fierce attacks of nature that produce erosion. Now we have to grope blindly for a while, as the wise ones do not have facts enough upon which to speak with definite certainty. But it is assumed that a great warping of the earth's crust took place, and that in this revolution some of the plateau sank,--supposedly the northern part, though it certainly extended across the Canyon nearly as far south as Williams and Ash Fork, and other parts--the edges--arose, and thus formed a basin which became another vast inland sea.