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Show THE TEIASâ€"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 thickness 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 predominant hue being a bright lively red, often inclining to orange. Occasionally, 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 Shinarump, and, furthermore, change from red to brown along the course of a single laj^er or bed, while in the Shinarump every layer preserves its color without a trace of change through many miles of exposure. The predominant 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 distance 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 1,500 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 Shinarump below and the Jurassic above. Let us recall here that the series is composed 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 |