OWL CREEK MOUNTAINS 553 



half-inch or more on the rock surface as a ragged network, the purer rock 

 between having been dissolved. This feature and the very massive bedding 

 are as characteristic here as in the Bighorn mountains. In the canyons 

 the formation gives rise to steep walls, presenting almost continuous out- 

 crops of the formation, a feature strikingly exhibited in Owl Creek canyon 

 as shown in figure 2, plate 76. Here the massive limestone is overlain by 

 20 feet of white, broken limestone capped by a 20-foot massive bed similar 

 to the thick limestone below. At the top of the formation there are a few 

 feet of sandstone and shale, which are directly overlain by Madison lime- 

 stone. In places the upper beds weather to a reddish tint, strongly sug- 

 gestive of the member of Eichmond age, which occurs in the northern 

 portion of the Bighorn uplift. In figure 1, plate 77, is shown the basal 

 contact of the massive limestone with the Deadwood shales, the top Dead- 

 wood limestone being absent. 



Very few fossils were found in the Bighorn limestone in the Owl Creek 

 mountains, and these were fragments of maclurinas and corals similar to 

 those in the Bighorn mountains. 



Ordovician in Northwest Wyoming and Montana 



West of the Bighorn basin lie the Absaroka and Shoshone mountains, 

 consisting of Tertiary rocks, mainly igneous, which cover the older forma- 

 tions. In an outlying range known as Cedar and Eattlesnake mountains, 

 west of Cody, the lower Paleozoics appear and the Bighorn limestone is 

 present. It has been studied by Mr C. A. Fisher,* who states that the 

 thickness is 150 feet and the formation presents its usual character and 

 strati graphic relations, excepting that the reticulating network of silica 

 on the weathered surface of the rock are less pronounced than in the Big- 

 horn mountains. The upper portion of the formation consists of thin 

 bedded limestone not sharply separable from the overlying Madison lime- 

 stone. Outcrops occur in canyons of the Shoshone river, Clark fork, and 

 Pat O'Harra, Little Bocky, Bennett, and Line creeks. 



On the east slopes of the north end of the Absaroka range there is an 

 extensive development of Paleozoic rocks, which has been described by Mr 

 Arnold Hague in the Absaroka folia. f On the Cambrian (Gallatin lime- 

 stone) lies the Jefferson limestone, which is classed as Silurian, but no 

 satisfactory paleontologic evidence of its age was obtained. From the 

 descriptions given in the folio this limestone appears not to closely re- 

 semble the Bighorn limestone exposed lower down Clark fork and in 



* C. A. Fisher : Geology and water resources of the Bighorn basin, tJ. S. Geol. Survey, 

 Professional paper no. 53. 



t U. S. Geol. Survey, Geologic atlas of the United States, folio no. 52, 1899. 



