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Show 212 EXPLORATION OJ.J' THE OANONS OF THE COLORADO. thousand five hundre~l feet iu thickness, and beneath them we have a thousand feet of conformable rocks of undetermined age. This gives us 4,500 feet, from the summit of tho plateau down to the non-conformable beds. Still beneath these we have 1 ,5UU feet, so that we have more than one thousand five hundred feet of other rocks exposed in the depths of the Grand Calion. Standing on some rock, which has fallen from tho wu.ll into the river-a rock so large that its top lies above the water-and looking overhead, we see a thousand feet of crystalline schists, with dikes of greenstone, and dikes and beds of granite. llerotofore we have given the general name granite to this group of rocks; still, above them we can 8ee beds of hard, vitreous sandstone of many colors, but chiefly dark red. This group of rocks adds but little more than five hundred feet to the height of the walls, and yet the beds are 10,000 feet in thickness. How can this bo~ The bedH themselves are non-conformable with the overlying Carboniferous rocks; that is, the Carboniferous rocks are spread over their upturned edges. In Illustration 79 we have a section of the rocks of the Grand Canon . .A, .A represents the granite; a, a, dikes and eruptive beds; B, B, these nonconformable rocks. It will be seen that the beds incline to the right. The horizontal beds above, C, C are rocks of Carboniferous Age, with underlying conformable beds. The distance along the wall marked by the line x, y, is the only part of its height represented by these rot.ks, but the beds are inclined, and their thickness must be measured by determining the thickness of each bed. This is done by measuring the several beds along lines normal to the planes of stratification; and, in this manner, we find them to be 10,000 feet in thickness. Doubtless, at some time before the Carboniferous rocks C, C were formed, the beds B, B extended off to the left, but between the periods of depoRition of the two series, B, B and c, c there was a pel'iod of erosion. rrhe beds, themselves, are records of the invasion of the sea; the line of separatiou, the record of a long time when the region was dry land. 'l'he events in the history of this intervening time, the period of dry land, one might supp•)Se were all lost. What plants lived here, we cannot learn; what animals roamed over the hills, we know not; and yet there is a history which is l)Ot lost, for we find that after these bed~:; were formed as sediments beneath the sea, and still after they had been folded, and the sea had left them, and c .B Fi~otu t·o 79.-Scction of wall in tho Gmuu Cu.t1ou. |
