PEALE.] DESCRIPTIVE GEOLOGY — SUBLETTE RANGE, 581 



ivg from what we saw south and north of it, its component rocks are of 

 Jurassic age, which are folded as they are to the south. In the northern 

 portion of the south end of the range, Station 38 is located. A frag- 

 ment of a Za^hrentis from the station was brought in, which indicates 

 that the centre of the range is Carboniferous. The exposures of rocks 

 are very limited. Bast of Station 38 Jurassic limestones dij) to the 

 eastward, and on the west red sandstones are seen dii^ping sharply to 

 the westward. The range is therefore a sharp anticUnal, with perhaps 

 a slip on the west. Following the ridge of the station southward, we 

 find that it becomes eroded into a number of peaks with round summits, 

 which end five miles south of the station, on the north side of a branch 

 of the Bear, that rises in the range east of these peaks. On the east 

 side of this creek we find the range continued in a ridge which is com- 

 posed of Jurassic limestones representing the eastern members of the 

 anticlinal fold. At the north end of the ridge is a peak which connects 

 it with the range. Here the following were obtained : 

 Fentacrinus asteriscus^ 

 Caniptonectes helUstriatuSj 

 which prove the Jurassic age of tlie layers. Pentacrinus asteriscus 

 was also found at several other points in the ridge. 



This ridge is about three miles in length, and ends against a branch 

 of the creek which separates it from the main range. South of it is a 

 collection of rather broad-topi)ed hills, rising about 1,800 feet above the 

 Bear, and in their strata dips to the westward were seen. It would 

 therefore seem to be the westei'u side of another anticlinal fold, for in 

 Ooketown Butte and east of it the dips are all to the eastward in the 

 Jurassic rocks, while the butte itself shows the anticlinal in the (3arbo- 

 niferous limestones. At first I was inclined to consider the latter fold to 

 be the same as that in the main range, but there are indications that the 

 strike is a little east of north, which would carry the axis east of that 

 shown at Station 38, and render it probable that this fold is the same 

 as that of Station 41, which is 22 miles north on a branch of Thomas' 

 Fork. The folds are sharper towards the south, and we have seen that 

 the limestones in the centre of the antichnal dip 80°^ and that the coal- 

 bed in the Laramie Group stands on end. In the region of Station 41 

 the greatest dips do not exceed 40°, and are generally only 25° or 30°, so 

 that the folds have become much broader, and the older beds do not 

 appear, the sandstones of the Laramie '? Group forming the surface 

 rocks. 



However, before it can be asserted that the folds are identical a sec- 

 tion must be carried directly east from Station 38 to Smith's Fork. 

 East of the station there is a high, somewhat-rounded hill, that is proba- 

 bly on the axis of the fold, and another similar one south of it appears 

 to continue the hue towards Coketown Butte. What the connection is 

 between the Jurassic and the Laramie I am, in the absence of fossils 

 from the intermediate beds, unable to determine positively, although I 

 think the Cretaceous is present. The valley of Bear Eiver between 

 Smith's Fork and Thomas' Fork is comparatively narrow, widening out 

 as we approach the latter stream. In two small hogback ridges on the 

 west side of the Bear, below the n)oulh of S:iiilh'd Fork, the rocks show 

 westward or northwestward dips. They jnobably represent a portion 

 of the anticlinal of Coketown Butte. 



TnO]MAS' PORK. 



Thomas' Fork is a large and important branch of the Bear. It drains 

 the country north of the Sublette Eange as far as Crow and Beaver 



