328 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



that the upper portion of Mount Floyd consists of strata which are higher in the series, 

 probably Upper Carboniferous. In this and also the next range west of Rush Valley 

 no igneous rocks were observed, but the dip there, like in all the mountains of the 

 district in general, is variable, and changes frequently within short distances, appar- 

 ently depending upon local concentration of the subterranean forces at different points 

 of these ranges. 



Cedar Valley and Rush Valley form separate basins. The spur of hills in the 

 latter valley also consists of rocks of the Carboniferous formation, but on the road to 

 General Johnston's Pass, east of Meadow Creek, we pass over low outcrops of sand- 

 stones, which, although tilted at an angle of 45 degrees, present a quite modern ap- 

 pearance, and seem to be a local formation. Still I am doubtful in regard to their age, 

 not having found any fossils. Near the creek I noticed a low outcrop of fine white 

 friable sandstone, or rather scarcely indurated sand with interstratifications and irregu- 

 lar secretions of gray, hard, brittle, siliceous rock which looks as if it was hardened 

 from gelatinous silex, and is apparently formed from the sand by influence of alkaline (?) 

 water, and of modern (lacustrine) origin. 



The mountains west of Rush Valley consist of limestones, &c, like the last ones. 

 The fossils collected in the various passes are mostly corals, and seem to belong to 

 the Lower Carboniferous period. The strata in many instances exhibit strong marks 

 of violent dislocations and altering influences, either heat or chemical agencies. Some 

 appear as if crashed into fragments and then recemented into a regular breccia. In 

 Oak Pass, high exposures of an altered sandstone were noticed, of nearly porphyritic 

 appearance. 



We next enter Skull Valley, or by the more southern passes, another branch of 

 the Great Salt Lake Desert, separated from the former only by a low sand ridge. A 

 chemical test showed the efflorescences of salt around Willow Spring to the pure chlo- 

 ride of sodium. 



The next range of mountains of considerable extent from north to south, is Colo- 

 nel Thomas's range, of which the Granite Mountain forms the northern prolongation. 

 In the intervening country we find some more isolated mountain masses and numerous 

 island mountains. Southwest of Willow Spring the hills are composed of altered sili- 

 ceous limestones and sandstones, with remains of Gasteropoda, Brachiopoda, Corals, and 

 Bnjozoa, of < 'ail ,, mit'erous age. Further south Igneous Rocks partake in the formations. 

 The central portion of Mount Champlin is composed of the porphyry, No. 181, of the 

 collection, which I have mentioned above (see under Igneous Rocks), and other rocks 

 allied to the tracliytic porphyries. Near the base of these mountains I noticed also 

 other rocks, forming dikes and smaller outcrops of perhaps later origin, also vesicular 

 rocks ot dark color. All around the mountain, partly covering the igneous rocks, 

 partly as separate, more or less distant, island buttes, stratified rocks were observed, 

 mostly m a highly altered state, limestones, slates, and especially a dark reddish-brown 

 Biliceous sand-rock, which at some points attains a quite porphyritic appearance. The 

 McDowell Mountains, further southwest, with their characteristic peaks, are nearly 

 altogether composed of eruptive rocks similar to those of Mount Champlin. They 

 exhibit a most interesting transition among themselves, and between extreme tvpes at 



