The Grand Canyon Of Arizona: How To See It By George Wharton James

 -  All these zoics have to do with life. Proterozoic means before
life, and signifies the rocks that contain no fossils - Page 67
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All These "Zoics" Have To Do With Life.

Proterozoic means before life, and signifies the rocks that contain no fossils indicative of life; Paleozoic signifies the most ancient forms of life; Mesozoic signifies "middle life" or those between the most ancient and the Cenozoic, or recent forms of life.

The periods are lesser divisions of the eras. In the Proterozoic, there are two periods, viz.: the Archaean and the Algonkian. The Paleozoic has six periods, viz.: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. The Mesozoic era has three periods, the Triassic, Jurassic and Cretaceous, while the Cenozoic era names five periods, - the Eocene, Oligocene, Miocene, Pliocene and Pleistocene.

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.

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