EXPLORATIONS ACROSS THE GREAT BASiN OF UTAH. 



Measant Valley, in this range, scorns to follow the line of contact between 

 Tons and metamorphic rocks. A conglomerate is found in the pass above 

 xstly composed of more or less rounded 





genera! nmiiguranou, ,r is pronaniN 

 fountains a considerable quantity 



and re-appear in the adjoining Crosman Vallev^&c. 



Next follows the Un-go-we-ah range, between Antelope and Steptoe Valleys, al/K> 

 of great altitude and extent, in which stratified Paleozoic as well as plutonic rocks 

 were observed. On the southern road we find on the east side a great thickness of 

 bluish gray calcareous slates and siliceous limestones, and, toward the summit, with 

 them a calcareous conglomerate, and a trachytic porphyry allied to that from the 

 McDowell Mountains. On the west side limestones are still more extensively developed, 

 mostly siliceous, and of dark bluish and gray color; also slates," and some sandstones. 



were obtained, indicating the Upper Carboniferous age, while others, from the western 

 portion of the range, seem to be Lower Carboniferous. Near the northern road, the 

 brown dioritic porphyries form the bulk of the mountains, while the stratified rocks, 

 bluish gray siliceous limestones, and sandstones altered into flint rock, are confined to 

 the highest summit and part of the western slope. We noticed some interesting in- 

 stances of the changed appearance of the rocks at the contact between the porphyry 

 and stratified rocks. Near our camp, in Spring Valley, in this range, highly peculiar 

 rocks were exposed, which seem to be the result of a later intrusion, partly pitchstones, 



fragments. They contain numerous light brown secretions of the size of a pea, with 

 a radiating structure, in the center of which frequently a small grain of feldspar can 

 be observed; they also contain some crystals of black mica. Higher up toward the 

 summit 1 noticed a local formation of conglomeratic rocks composed of igneous ma- 

 terial, and a high knob ot porphvrv, closelv allied to the porphyry from Simpson's 

 Spring at Mount Champlin. 



The Mont-tim range, between Steptoe Valley and Butte Valley, is composed of 

 some granite, more recent eruptive masses, and 

 sedimentary rocks of the Paleozoic age. Near tl 

 side of the mountains, bluish and gray siliceous 1 

 careens spar, slates, &e., petrographicallv much 1 

 Canon, but, as some fossils, Trilohites of the genei 



the pass. Although this is the first point where Devonian strata were noticed, they 

 may occur also farther east, having escaped observation on account of the similarity 

 of their Hthological character with that of Carboniferous strata and the scarcity of fos- 

 sils. A considerable thickness of flint-rock and altered sandstone was exhibited in and 

 near Egan Canon, probably underlying the Devonian limestones, and also strata of 



mctamo 



rphosed 



strata, but i 



chiefly of 



ike the 1 



ra Homa 



es threa 

 brmafio 

 lonotus a 

 unappe 



de^witb'vei 

 us in the Til 

 nd Proetus, 

 ar near the i 



ns of cal- 

 npanogos 

 prove, of 

 summit of 



