150 GEOLOGICAL SURVEY OF THE TERRITORIES. 



CHAPTER IX. 



FROM FORT HALL— SODA SPRINGS— BEAR-RIVER VALLEY— BEAl^-LAKE 

 VALLEY— TO EVANSTON ON UNION PACIFIC RAILROAD. 



I will not delay, at this time, to discuss the many interesting prob- 

 lems connected with the great basin of Snake Eiver. Further examina- 

 tions will add greatly to the observations we now possess. Indeed, it is 

 hardly possible, in these preliminary rei)orfcs, to do more than to make a 

 brief record of field-notes. The great lines of thought which are opened 

 up in every direction by the wonderful phenomena of this singular re- 

 gion must be followed persistently to their legitimate conclusions. Time 

 and careful study will be required to work out all the results, and these 

 cannot be given at this period. Our barometric observations indicate 

 the altitude of Fort Hall to be 4,720 feet above the level of the sea. 

 This will form our starting-point homeward from the basin, and, inas- 

 much as most of the way will be toward higher altitude, we may thus 

 know the grade from point to point. 



On our way up to Fort Ellis, in June, we ascended the Cache Yalley, 

 and, passing the divide, descended one of the more western branches of 

 the Port Nenf into the Port Neuf Canon ; then iuto the Snake River 

 Basin. On our return , we crossed the divide between the Blackfoot Fork 

 and the Port Neuf, 5,904 feet, down into a broad valley, a kind of synclinal 

 depression between the high ranges of mountains. In this valley, the 

 sources of the main branch of the Port Neaf gather together before 

 cutting through the ranges of mountains. 



I have, in a i)revious chapter, noted briefly the formations along the 

 east side of the Snake Basin, in the vicinity of Fort Hall. The Jurassic 

 and Carboniferous groups of strata form the bulk of the sedimentary 

 rocks, with the Pliocene or Lake deposits jutting up into the ravines or 

 valleys, and sometimes occurring high up on the sides of the mountains. 

 The range of mountains which formed the eastern wall of the Cache Valley 

 in its northward extension seems to have broken up into irregular frag- 

 ments after reaching the rim of the basin, and, with the exception of a 

 few rather high peaks, seldom reaches an elevation of more than G,000 or 

 7,000 feet on the east border of the basin. I did not observe rocks of 

 Cretaceous or Lower Tertiary age here, though I think a more careful 

 examination will reveal them. Originally there was a system in the 

 formation of the mountain hills on the east side of the basin, but subse- 

 quent to their upheaval the outbursts of igneous material have produced 

 apparent chaos. The sedimentary^ formations at this time incline in 

 every direction and at all angles. 



After crossing the divide, we descended into an open, grassy valley, 

 extending to the northern bend of Bear River, averaging about three 

 miles in width, but expanding, near the point where the sources of the 

 Port Neuf unite and cut through the mountains, to a width of five miles. 

 On the east side, the range of hills is entirely composed of Carbonifer- 

 ous Imestones, so far as I could ascertain after a careful examination. 

 This range of hills is composed of broken ridges, which rise for 800 to 

 1,500 feet above the level of the valley. One ridge, which I measured 

 witt care, as an average, was 1,100 feet. In many localities these lime- 

 stones were charged with fossils. In no portion of the Rocky Mountain 

 Range have I seen them of greater abundance and variety. Quite thick 

 layers of a compact, bluish limestone were entirely composed of corals 

 and crinoidal stems. In the valley itself the basaltic covering is ex- 

 posed here and there, though it is not quite as conspicuous as it is 



