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Show 22 INTRODUCTORY. of the rocks. The Pliocene witnessed the gradual development of an arid climate similar to that now prevailing there; To this age belong the canons and the great cliffs, which could not have been produced in an ordinary or humid climate, nor at low altitudes. That this aridity is by no means a condition of recent establishment is indicated by many evidences. They consist of remnants of a former topography, preserved in a few localities from the general wreck of the land, and which show the same general facies of cliffs and canons as those of more recent formation. And as the more recent sculpture owes its peculiarities in great part to the aridity, so, we conclude, must these more ancient remnants The Kaiparowits Plateau presents an excellent example. Its surface is in many places rendered utterly impassable by a plexus of sharp narrow canons, of which the heads have been cut off by the recession of the gigantic cliff which forms the eastern wall of the plateau. They have long been dug, and have remained with but little change for an immense period of time. And now the relation of the High Plateaus to the Plateau Province at large becomes evident They are the remnants of great masses of Tertiary and Cretaceous strata left by the immense denudation of the Plateau Province to the south and east. From the central part of the province the Tertiary beds have been wholly removed and nearly all of the Upper Cretaceous. A few remnants of the Lower Cretaceous stretch far out into the desert, and one long narrow causeway, the Kaiparowits Plateau, extends from the southeastern angle of the district of the High Plateaus far into the Central Province and almost joins the great Cretaceous mesas of Northeastern Arizona, being severed from them only by the Glen Canon of the Colorado. The Jurassic has also been enormously eroded. This formation, which i>' d great importance and bulk in the northern and northwestern portion of the province, and especially around the High Plateaus, appears to have thinned out towards the south and southeast. ]n large portions of New Mexico it is wholly wanting and was probably never deposited there. In the northwestern portion of that Territory only a few thin beds of that age are found. But in the northern part of the province a conspicuous and wonderful sandstone formation of most persistent character is found, overlaid and underlaid by shales holding a distinctly Jurassic |
