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 ap- 

 proach 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 Piivant, 

 at least, plicated and contorted Carboniferous rocks still overlook the Ter- 

 tiary beds, with every indication that this relation has remained unaltered 

 throughout Tertiary time, though general movements of displacement in- 

 volving the entire range have othei-wise modified its topography. Like all 

 rockbound coasts it had its sinuosities — 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 east- 

 ern flank of the range, near Marys vale, and thence southward for 10 miles, 

 we find the base of it to be composed of metamorjjhosed 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 reveal- 

 ing 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- 



