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he 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 masses 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 masses； some day to be mountain peaks； that refuse to sink again into the sea。 Then the forces of the air assail 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 masses 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 masses； 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 whilea few hundreds or thousands of yearsand the masses 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 redsalmost crimsonsof 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 pronounce； 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 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…bedscarbon 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 cert