406 ~ N. H. DARTOK PALEOZOIC AND MESOZOIC OF WYOMING 



Bighorn and Owl Creek uplifts, which have been published by the gov- 

 ernment.^ ^ 



It is the purpose of this memoir to present an outline of the results 

 which throw light on the classification and general stratigraphy of forma- 

 tions from Cambrian to Cretaceous in age. Tertiary deposits exist 

 throughout the area examined, but only passing attention was given to 

 their features, and the various formations are not differentiated on the 

 geologic map, plate 21. 



General Geology 



The sedimentary rocks of central Wyoming represent parts of Cam- 

 brian, Ordovician, and Jurassic time and nearly all of Carboniferous, 

 Cretaceous, and Tertiary time. The Triassic apparently is represented 

 also, but only in part. The table on page 407 is a list of the formations, 

 with brief notice of their character and ordinary range in thickness. 

 Some general comparisons of the stratigraphy are shown in plate 33. 



General Stratigraphy 



The pre-Cambrian rocks are overlain unconformably by the Cambrian 

 and later sedimentary rocks, and in most places were planed very smooth 

 before the sediments were laid down. Although some of the Paleozoic 

 and Mesozoic strata are separated by erosion unconformities, no discord- 

 ance of dip is perceptible. The Deadwood formation, representing a por- 

 tion of middle Cambrian-Acadian time, is present throughout northern 

 and central Wyoming, but does not extend into the Laramie Mountain 

 region. The Bighorn limestone, the product of part of Ordovician time, 

 is restricted to the Wind Eiver-Owl Creek and central and northern Big- 

 horn regions. Silurian and Devonian do not appear. The Carboniferous 

 comprises the Pennsylvanian and Mississippian divisions in the greater 

 part of the region, but the latter thins out to the south and ceases in 

 Laramie mountains along a line not definitely located. This line crosses 

 the range not far from the canyon of Laramie river. The Pennsylvanian 

 division, which consists mainly of shales and sandstones in northern 

 Wyoming, contains thick bodies of limestone east of longitude 107°, but 

 on both sides of Laramie mountain south of the latitude of Laramie these 

 mostly give place to sandstone largely of red color. The Chugwater red 

 beds, consisting of fine-grained bright red sediments, with gypsxTm de- 

 posits and thin limestone layers, underlie the entire area. The marine 



" U. S. Geological Survey Professional Paper no. 51. Washington. D. C, 1906. 



* gist Congress, 1st session, Senate Executive Document no. 219. Washington, 1906. 



