the grand canyon of arizona-第22部分
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nds。 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 partsthe edgesarose； 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 principal 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 mass 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 Washington 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 ithence the law that geologists call 〃the persistence of rivers。〃 By and by； the uplifted country appeared as one vast area of river valleys； separated by stretches of plateau。 Little by little； working by laws that are pretty well understood； the swift flowing avers cut downwards。 When their velocity ceased； the widening of the river courses began； and progressed with greater rapidity； so that； in time； the divides that intervened between the rivers were worn away；a process rudely shown in Fig。 5 A。 B。 C。 and D。 of plate on page 110。
The Formation of the Canyon。 Now； in imagination； let us hark back to the day when this plateau was in the condition thus described。 Nearly everything in the way of strata has been planed down to the Carboniferous rocks。 The plateau is about at sea level。 One great river already exists； with two arms； now called the Green and the Grand； the main river some day to be known as the Colorado。 Slowly the uplift begins。 It is a fairly even process； and yet there is slightly more pressure brought to bear under the southern portion； so that the whole mass has a slight tilt to the north。 Professor Salisbury found certain beds of rock at seven thousand eight hundred feet above sea level at the base of the San Francisco Mountains near Flagstaff。 Forty…five miles north； at the Grand Canyon； these same beds are only six thousand four hundred feet above sea level； while at the Vermilion Cliffs； another forty…five miles to the north； they are but four thousand four hundred feet above the sea。
Yet in spite of this northward tilt； when the eye ranges over the country to the south and west； from the upper porch of El Tovar； a large area of depression can clearly be seen； showing that surface erosion has planed away much of the upper crust。
The Plateau Region。 Now we are ready to take a look at the borders of the plateau region。 On the north； it extends into Utah； where still higher plateaus bound it。 To the west； it extends by gigantic steps into the desert region。 The main step is along the Grand Wash； near the one hundred and fourteenth meridian。 To the south； there is one glorious step； known as the Mogollon Escarpment （locally the Red Rock Country）； some three thousand feet high； which extends for a number of miles east and west； and then breaks down。 This step and broken levels lead to the irregular lands of Central and Southern Arizona。 On the east； the plateau extends to the Echo Cliffs beyond Marble Canyon； and as far as the ridge of the Continental Divide； where the Santa Fe crosses the Zuni Mountains； east of Gallup； N。 M。
Present Conditions。 With this general view of the great plateau in our mind's eye； we are prepared to examine present conditions at any given spot in the Canyon。 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 ar
