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Show 184 GEOLOGY OF THE HIGH PLATEAUS. The Tushar stands upon the course of the western shore line of the great Eocene lake. This shore line may be traced, with a very close approach to exactitude, from the southern base of Nebo across Juab Valley to the Pavant, and through that range longitudinally as far as the northern flank of the Tushar. For the whole series of lacustrine beds may be seen abutting sharply against the disturbed beds of Carboniferous and early Mesozoic age along this line, excepting where their junction is concealed for a short distance by the alluvia of the Juab Valley. Through a portion of its extent this fragment of the coast was rockbound; for in the Pavant, at least, plicated and contorted Carboniferous rocks still overlook the Tertiary beds, with every indication that this relation has remained unaltered throughout Tertiary time, though general movements of displacement involving the entire range have otherwise modified its topography. Like all rockbound coasts it had its sinuositiesâ€"here an estuary, there a peninsula; here a bight, there an outward swing of the shore. This coast line strikes the Tushar near its northwestern angle and is instantly lost beneath floods of rhyolite. Nothing is seen of it until nearly 50 miles south-southwest it is revealed in the Iron Mountains by Tertiary beds cut off against the Trias. If we suppose a straight line joining the broken ends to represent the mean position of the coast line, the whole of the Tushar would stand within the Eocene lake; but this supposition is not tenable. On the eastern flank of the range, near Marys vale, and thence southward for 10 miles, we find the base of it to be composed of metamorphosed quartzites, upon which a few patches of limestone rest, holding Pentacrinus asteriscus, a highly characteristic Jurassic fossil, and upon this quartzite and limestone immediately rest the lavas. No trace of a Tertiary or even Cretaceous stratified rock is to be seen. The uneven eroded surface of these beds, with hills and valleys and rocky eminences, was thus sealed up at the very epoch of which we speak and broken open at an epoch long subsequent by the shearing of a great fault and by the cutting of ravines, thus revealing in a manner which cannot be mistaken the existence of a land area. It lies at least 15 miles to the eastward of the straight line joining the broken ends of the lake coast. Either, then, we have a peninsula or an island in the lake to mark the nucleus of the future Tushar. The Tertia- |