18 GEOLOGI.CAL SURVEY OF THE TERRITORIES. 



range of mountains, wliich ^re call the Wahsatch Eange, was originally 

 a complete anticliual fold, then it forms a fine illustration of the erosive 

 eifects of water in comparatively modern geological times, which for so 

 great a distance has swept away the entire half of the range. We may 

 also suppose that beneath the great thickness of superficial deposits which 

 compose the terraces, the edges of the strata which form the west side of 

 the fold now exist, dipping beneath the valley, but rising again on the side 

 of some other fold in the basin as Antelope Island, &c. If our suppositious 

 are true, the -next question that at once arises in the mind would be as to 

 the cause of this tremendous erosion. We have neither space nor time, 

 even if we had all the facts, to discuss this most interesting problem in 

 the present report, but we promise our readers to recur to it again at 

 some future time. We may, however, suppose that the Wahsatch Range 

 formed the eastern shore of the great inland sea which, at a compara- 

 tively modern geological period, covered the entire basin. How great a 

 depth it ever attained it is difficult now to determine, but at some period 

 its waters must have reached high upon the sides of the loftiest ranges, 

 so that they appeared scattered here and there as islands projecting 

 above the surrounding waters. It is probable that during the gradual 

 decrease of the waters of this lake the greater portion ot the erosion of 

 the caiions was performed. Up the valleys of all the little streams that 

 lead into Salt Lake are the terraces and peculiar lake-deposits, showing 

 that the lake-waters extended far up beyond the wall-like shores. It is 

 altogether probable, from the proofs which are found everywhere in 

 these valleys, that there were continued oscillations in the depth of the 

 lake-waters, a rise and fall, and long periods when the waters would 

 remain at a fixed level. If we take tlie position that the present results 

 of erosion have all been brought about b.'v the slow destruction of the 

 rock-materials by water, and that this force is produced by the agita- 

 tion of the waters beating upon the shores, then we may suppose that 

 the winds from the west and southwest prevailed and gave to the waters 

 the force that slowly pi-oduced the erosive results that we now see on 

 the east and northeast sides of the valley. Other causes may have 

 united in producing these results, which we hope to present at some 

 other time. 



From Salt Lake Valley the Snake Eiver division of the survey pro- 

 ceeded northward, by way of the parallel valley, to the valley of Snake 

 River near Fort Hall. In my report for Jl871, I recorded most of our 

 observations on this route, and now refer the reader to the more com- 

 plete account of Professor Bradley in this report. 



x\.s we proceed northward toward the divide between the waters of 

 the basin and Snake River, the quartzites seem to diminish and the cal- 

 careous beds to increase, and the conditions seem to have been more 

 favorable for the preservation of organic remains. The Oarbouiferons 

 limestones seem to be well developed, and charged in some jdaces with 

 characteristic fossils. On the divide between Ross Fork and Lincoln 

 Valley, near Fort Hall, Professor Bradley obtained a stray mass of 

 limestone, in which was crowded together a mass of minute fossils, nearly 

 forty species, many of them identical with species found at Spergen Hill, 

 Indiana. (See Catalogue of Fossils, by Mr. Meek.) This is certainly a 

 m@st important discovery, extending the existence of this formation 

 very much farther west than it had ever been known before. Previous 

 to this time not a single species of this group had been found west of 

 Iowa or Missouri. It indicates that quite probably, if the great mass of 

 Paleozoic rocks of the West could be examined in detail, they might be 

 separated into numerous subdivisions, as we find them where they have 



