22 mTRODUCTORY. 



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 Prov- 

 ince 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 North- 

 eastern Arizona, being severed from them only by the Glen Canon of the 

 Colorado. The Jurassic has also been enormously eroded. This forma- 

 tion, which i'- *f great importance and bulk in the northern and north- 

 western portion of the province, and especially around the Pligh Plateaus, 

 appears to have thinned out towards the south and southeast. In 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 char- 

 acter is found, overlaid and underlaid by shales holding a distinctly Jurassic 



