178 GEOLOGY OF THE HIGH PLATEAUS. 



The eastern front of the Tushar preserves that rugged mountainous 

 aspect ah'eady described thi'oughout two-thirds of its extent. The southern 

 third is a wall of imposing grandeur, presenting to the eye the effect of a 

 perpendicular escarpment, though really it is inclined at a slope of 60° or 

 more. It is a magnificent object as seen from Circle Valley, rising nearly 

 2,000 feet above its base, and its base standing at the summit of a long 

 slope which rises 2,000 feet above the valley bottom. This great cliff is a 

 conglomerate composed of the ruins of older volcanic rocks. It is stratified, 

 but not so conspicuously as most of the similar formations so abundant 

 throughout the district. The finer material which incloses the rocky frag- 

 ments is a light-gray pulverulent detritus, evidently resulting from the 

 decomposition of feldspathic materials and highly aluminous. Some of the 

 members of this series of heavy beds consist chiefly of this finer material, 

 holding comparatively few fragments ; in others the fragments are much 

 more abundant, constituting the greater part of the mass. The fragments 

 are usually somewhat rounded at the edges, but in most cases the amount 

 of attrition is small, though seldom wholly unrecognizable. The mode of 

 origin of this and similar conglomerates will be discussed in detail in a sub- 

 sequent chapter. It is a sub-aerial formation throughout, and the mode of 

 accumulation may be seen and studied hard by in all the valleys of the 

 district. (See Heliotype II.) 



These beds are of ancient origin, having been formed prior to the 

 great displacements which have given the Tushar its present structural 

 features. The inclosed fragments are wholly variable in character. None 

 of the rhyolitic, trachytic, and basaltic rocks of later age are seen among 

 them, and the inference is irresistible that its formation was completed before 

 these last-named masses were erujjted. The source of these materials seems 

 to have been the adjoining mass of the present Tushar table to the north- 

 ward. To realize how this may have been we are obliged to go back in 

 time to the later Eocene or early Miocene, when, in all probability, these 

 great outbreaks occurred, and endeavor to reconstruct the country. At 

 that time the centers or loci of eruption were doubtless in the very heart 

 of the range, and stood considerably higher than the adjoining part of the 

 country, just as they do now, though, more recent movements on a grand 



