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Show 150 GEOLOGY OF THE HIGH PLATEAUS. and cleaves off by its vertical joints. Take now a series of these alternating massive layers and softer shales, the long process of erosion gives a series of perpendicular walls, alternating with sloping taluses. This composite architecture is one of the most persistent features of the formation. Something like it is seen in the Carboniferous strata forming the walls of the Marble Canon of the Colorado, but there are also many wide differences both of detail and ensemble. niiiijjjjuuLuuuiL 3 â- -• i iSjrLj^icQjjznLJiun ' i r,f tT-iTtr" i^ggBsiaffl Fig. 3.â€"Generalized profile of Vermilion Cliff. The thickness of the Upper Trias is from 1,100 to 1,800 feet, being greatest in the vicinity of the old shore line, and very slowly attenuating to the eastward. THE JURASSIC. The Jurassic series consists of two members, the lower being a massive sandstone of great thickness, the upper a series of calcareous and gypsifer-ous shales from 200 to 400 feet thick. Underneath the sandstone is a small group of shaly beds, which are presumed to be of Jurassic age, but no determinable fossils have been taken from them. It has been a long-standing and dimcult question whether the Jurassic sandstone is not, after all, a mere upward continuation of the Vermilion Cliff beneath. Much color was given to this supposition by the fact that no unconformity between them has been detected in this vicinity, and still more by the fact that as we travel eastward and southeastward from the High Plateaus the distinc- |
