THE TEIAS— VERMILION CLIFFS. 149 



trast in their respective aspects, and the geologist who studies them in the 

 field is constantly reminded of the distinctions. The Upper Trias consists 

 of many beds of sandstone with shaly partings. Usually the component 

 members do not attain great thickness, but a few of them occasionally have 

 a tliickness exceeding 200 feet. Very many of them are cross-bedded in 

 a beautiful manner, and although this feature is not so strongly marked 

 as in the Jurassic sandstone, it is almost always conspicuous enough to 

 attract attention. The whole formation is brilliantly colored, the predomi- 

 nant hue being a bright lively red, often inclining to orange. Occasionall}'-, 

 however, this color gives place to a strong yellow or bright brown. These 

 are very distinct from the deep crimson, chocolate and purple of the Shin4- 

 rump, and, furthermore, change from red to brown along the course of a 

 single layer or bed, while in the Shinarump every layer preserves its color 

 without a trace of change through many miles of exposure. The predomi- 

 nant red, approximating to vermilion, induced Professor Powell to give the 

 local name of Vermilion Cliffs to their grandest and most typical 

 exposure. 



The Upper Trias is in truth the great cliff-forming series of the Plateau 

 Country. No other formation equals it in the extent and variety of cliff 

 exposures. The Vermilion Cliffs extend from the Hurricane fault to Paria, 

 more than a hundred miles in a straight line, and more than twice that dis- 

 tance if we follow the sinuosities of their escarpment. Throughout this 

 distance they front the south with a succession of superposed ledges, rarely 

 less than 1,000 feet in height and often exceeding 1,600 feet; throwing out 

 great promontories, and deeply notched by estuaries and bays. Wherever 

 exposed in more easterly regions the same tendency to form cliffs may be 

 observed. These escarpments have their distinctive architecture and a 

 structure quite as peculiar to the formation as those of the Shindrump 

 below and the Jurassic above. Let us recall here that the series is com- 

 posed of manifold layers of sandstone, with many shaly layers intervening. 

 Usually three or four members are massive beds of very homogeneous 

 sand rock, with a thickness of 100 to 250 feet. Recall, also, that the most 

 effective attack of erosion is made primarily against these yielding shales, 

 while the overlying and more obdurate sand rock is thereby undermined 



