Part 8 (1/2)
Prior to the deposition of these Algonkian strata, the Laurentian rocks (the granite) upon which they rest were subject to a long period of ”planation,”--as the grinding down and leveling of rock surfaces is termed.
After this planation was complete, a subsidence occurred; the whole area became the bed of an inland sea, and upon the planed-down granite, the debris that formed the Algonkian strata was washed.
While they were being deposited, the whole region was the scene of several seismic and volcanic disturbances, for great d.y.k.es and ”chimneys” of lava are found, showing clearly that, by some means or other, the strata were broken and shattered, cracked and seamed, and that through these cracks the molten lava oozed--forced up from the interior of the earth. It spread out over the Algonkian rocks in small sheets or blankets, which here and there are still to be found to-day.
Tilting of the Algonkian Strata. 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 was.h.i.+ng 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 quant.i.ty 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 ma.s.s as the present distance in vertical height from El Tovar to the river! Where has it all gone?”
Naturally an answer to these questions is mere conjecture, as only from a study of the facts revealed underneath the present strata, can any comparative knowledge be gained of the conditions existent at that prehistoric age. There may have been one river, or a score, or any number between, and it is probable one or more rivers carried the Algonkian debris westward and deposited it, as the Colorado River (not brought into existence until centuries later) is now doing with the debris of the existent strata.
Another Subsidence. Now, a new era is about to dawn. Planed and smoothed off as they are, the Algonkian and Archaean ma.s.ses are to be submerged once more in the ever receptive ocean. A period of subsidence occurs, and the whole area is soon hidden under the face of the sea. But, all around these are ma.s.ses, some day to be mountain peaks, that refuse to sink again into the sea. Then the forces of the air a.s.sail them. If they cannot be drowned, they shall be gnawed at, smitten, cut and worried by the air, the chemicals of the atmosphere, the storms, the rain, the hail, the frost, the snow, and thus made to feel their insignificance. Slowly or rapidly, they yielded to this disintegrating process, and as the rocky ma.s.ses broke up, they were washed by the rills and streams into the bed of the sea, where they soon rested upon the tilted ends of the Algonkian strata and exposed surfaces of the Archaean ma.s.ses, waiting for them.
The Deposition of the Tonto Sandstones. The wise men tell us that this ocean was a salt sea, and that it was quite shallow while these new sediments were being deposited. Little by little one thousand feet of the sediments of this epoch were washed down, so that it is very likely that the tilted strata upon which they rested slowly sank lower and lower to accommodate them. Then, for some reason or other, there was a rest for a while--a few hundreds or thousands of years--and the ma.s.ses of sediments became cemented into sandstone and shale, which we call the Cambrian formation, or the Tonto sandstone. This is to be seen resting both upon the Archaean and Algonkian from the porches of El Tovar. It is composed of strata of dull buff, very different from the brilliant reds--almost crimsons--of the Algonkian, and the bright reds of the strata which later were to rest above them.
Geological Terms. What an audacious science this geology is! How ruthlessly it wrests aside the curtain from the mystery of the past, and how glibly it deals with thousands, millions of years, tying them up into packages, as it were, and handing them out labeled ”eras” and ”periods.” As usual, the names made by the wise men are hard to p.r.o.nounce, and seemingly hard to understand. But a few minutes will take away the difficulty. They divide the eras into four, viz.: 1, Proterozoic; 2, Paleozoic; 3, Mesozoic; 4, Cenozoic. 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 Tria.s.sic, Jura.s.sic 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 princ.i.p.al strata (with many smaller ones in between). The largest is the red-wall limestone, which const.i.tutes 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 circ.u.mstantial 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, Tria.s.sic, Jura.s.sic and even Cretaceous strata over the whole Canyon platform. Figure 4 of plate facing page 99.
Red b.u.t.te, 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 acc.u.mulation of much of the sediments of the Cambrian, Carboniferous, Permian, Tria.s.sic, Jura.s.sic 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 a.s.sumed 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.
Eocene Lake. We know this was an inland sea, and had no connection with the ocean, for all the fossils and sediments deposited in it reveal that they are fresh-water organisms. In this sea, as in the earlier oceans, vast deposits of sediment were made in the early Eocene period, and another period of subsidence occurred. Then the great lake was drained, and the uplift began, slow and sure; then, and not before, were the conditions existent that have made the Canyon country as we see it to-day. Peaks and islets received the rainfall, tiny rivers were formed that grew larger and cut their way in deeper, as the uplift continued. The princ.i.p.al stream, which was then born, was the Colorado. It is supposed, from various evidences, that the rainfall was very much more abundant then than now, and consequently the rivers had greater flow, and more eroding and carrying capacity. The uplift continued, and the geologists tell us it did not cease until about fifteen thousand feet, deposited since Cretaceous times, were thrust up into the air. As almost all this ma.s.s of deposition has disappeared from the immediate Canyon region, we are compelled to believe that it has been swept away down the Colorado River to join the sands of the Carboniferous and later periods in the Colorado Desert, the Salton Basin, the great low region of Lower California, and the Gulf itself.
Less by Erosion in the Canyon Region. Now figure out for a few moments the results of these different erosive periods. Eleven thousand five hundred feet of Algonkian gone; a small amount of erosion in the Cambrian epoch, the depth of which is unknown; and then the great denudation of the Eocene period sweeping away upwards of fifteen thousand feet of strata, give us a total of twenty-six thousand five hundred feet that have totally disappeared from the Canyon region. A vertical mile is five thousand two hundred and eighty feet. Mount Was.h.i.+ngton is about six thousand five hundred feet above the sea,--a trifle higher than Mount Lowe, near Pasadena, California. Take off from this six thousand five hundred feet, say one thousand five hundred feet, for the level of the country at the base of these two mountains, and then imagine a region five times as high as both of them, covering an area of country of possibly thirteen thousand to fifteen thousand square miles, slowly planed off by the erosive forces of nature.
Formation of River Beds. How was it done? I have spoken of the peaks and islets that first emerged from the Eocene Sea, and received the rains. 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.”