' CRETACEOUS SYSTEM 461 



Eor many miles along the foot of Medicine Bow and Sheep mountains 

 the Montana formation is faulted against the pre-Cambrian granites and 

 schists. Farther north, in Carbon county, it is overlapped by sandstones 

 which Mr Veatcli regards as a higher, or true Laramie, formation. In 

 this region Mr Yeatch divides the Montana into Pierre shale and Mesa 

 Verde sandstone, while the upper shale is regarded as equivalent to the 

 Lewis shale of Colorado. 



East of Laramie mountains. — At the foot of the mountains the Ter- 

 tiary is cut through by Crow, Lodgepole, and Horse creeks, and the Mon- 

 tana and underlying strata are revealed. The outcrop of nearly vertical 

 Pierre shale is over a mile wide on Horse creek. It gives place above to 

 gray sandstone in which the dip rapidly diminishes, so that only a few 

 hundred feet appear. This sandstone with low dips occupies a wide out- 

 crop zone west of the railroad, on the Middle and North forks of Crow 

 creek. 



Fossils. — Molluscan fossils occur in large numbers in the Pierre shale, 

 or lower division of the Montana formation, throughout central "Wyoming, 

 but very few were collected outside of Laramie basin. Fossil leaves occur 

 in the coal-bearing members, and, as shown by the geologists of the For- 

 tieth Parallel Survey, and again, ten years ago, by Stanton and Knowlton, 

 the marine Montana fauna, Pierre-Foxhills, recurs above the plant- 

 bearing beds.^" These latter observers examined the region lying between 

 Coopers creek and Eock river. A few miles southeast of Eock Eiver 

 station, where the sandstone associated witli the lower coal bed is 40 feet 

 thick, plants were olitained, -H-hile in shales 100 feet or more above were 

 found Barulites ovatus, Chlamys nehrascensis, and Inoceramus cripsii 

 var. harahini. Near the railroad cut along the foot of "Pine ridge," 2 

 miles southeast of Eock Creek station, where the same sandstone is 60 

 feet thick, additional plants were found, while in shale 500 to 600 feet 

 higher occur BacuUtes compressus, B. ovatus, Avicula nelrascana, and 

 some other forms. The shales below the prominent sandstone contain 

 many fossils, mainly in the thin beds of hard sandstone which are in- 

 cluded. Stanton and Knowlton gave a long list of typical Pierre fossils 

 from one bed 400 to 500 feet below the coal and from another horizon 

 300 to 400 feet lower. They also reported fossil plants from the lower 

 sandstone of the upper division of the Montana where it crosses Laramie 

 river at Dun's ranch, northwest of Howell, but the plants were not all 

 the same as in the region nearer Eock Creek station. Additional plants 

 were obtained at the small coal mine on the North fork of Button creek, 

 near the old stage road, where two of the species are the same as found 



'"Bulletin of the Geological Society of America, vol. 8, 1897, pp. 127-158. 



