290 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



from their general character, compared with those further east, we are inclined to con- 

 sider them as formed in the middle of the Tertiary epoch. No. 1 may correspond to 

 the green, shaly series overlying the Lignite formation on Platte River above Fort 

 Laramie, but they may just as well be altogether different, and deposited in separate 

 basins. At another point of this district we have found beds characterized by their 

 fossils, according to Mr. Meek, as estuary and Eocene Tertiary, which are tilted and 

 appear to be unconformable to these, therefore, more recent strata. 



From the sandstone series, No. 3, no fossils have been obtained. As nearly all 

 the older formations on the eastern slope of the Wahsatch Mountains, from the detritus 

 of which they must have been formed, are prevailingly arenaceous, we cannot find it 

 strange that the}' should lithologically resemble portions of them and still be more 

 modern. Wherever observed they are conformable to Nos. 1 and 2, and unconformable 

 to the older rocks. On the Quaking-Aspen ridge they cap unconformably the strongly 

 tilted coal-bearing strata, and on Bear River, near the mouth of Sulphur Creek, they 

 are nearly horizontal, like everywhere else, while close by the estuary strata are 

 strongly tilted. Although they present the general character of a somewhat older 

 formation, this close connection with the Fort Bridger strata seems to indicate that they 

 belong to the same geological horizon, and are only little older, perhaps Eocene. How- 

 ever, although they differ lithologically from the sandstones in the upper part of the Creta- 

 ceous Lignite formation, on the Upper North Platte River, near Bryan's Pass, they 

 may possibly be coeval with them ; that is, Upper Cretaceous. The greenish, shaly 

 sandstones, which appear to cap them there (see Lieutenant Bryan's expedition, 1856), 

 may correspond to the green series No. 1 (?). We cannot determine whether they 

 are of marine or fresh-water origin. 



From Green River eastward, the lithological character of the formation changes 

 somewhat, although it apparently forms the continuation of the Fort Bridger strata 

 The prominent table-hills, near the South Pass, must be composed of the equivalents 

 of No. 1. On the summit, and especially on the western slopes of the pass, above 

 Pacific Springs, strata crop out, which I consider as the continuation of No. 2, but 

 which contain a great deal more arenaceous material besides the lime, and perhaps, in 

 consequence thereof, attain a greater thickness. They form a series of white arenace- 

 ous limestones and calcareous sandstones, with interstratifications of loosely cemented 

 arenaceous shales and tine sand. Some of the harder ledges are compact siliceous 

 limestones with oolitic portions, like those further west ; but they are mostly a mixture 

 of sand and carbonate of lime, and closely resemble some of the strata of the Ash Hol- 

 low series. (Section II.) 



Red and green and brown coarse shaly sandstones, below the Pacific Springs, 

 and at several points further on, appear to be a local development of the formation,' 

 near the foot of the higher mountains. Along Big Sandy I noticed arenaceous and 

 some argillaceous shales, and lower down, some 20 miles from Green River, compact 

 sandstones overlying fine-grained shaly sandstones of white, yellowish, and brown 

 colors. These strata probably form the continuation of No. 3, but present a different 

 appearance, and resemble much more the rocks overlying the Lignite formation on 

 the upper course of North Platte River, east of Bryan's Pass, which there reaches 

 beyond the dividing ridge into the Green River Valley. 



