436 N. H. DARTON — STRATIGRAPHY OF THE BLACK HILLS, ETC. 



characteristic of the Mississippian, especially at about the horizon of 

 the Saint Louis limestone. It is possible that considerable of the lower 

 part of the Minnelusa is also of Mississippian age, for it appears to be 

 equivalent to the Hartville' limestone. The Littlehorn limestone of the 

 Bighorn uplift consists mainly of a representative of the Madison and 

 Pahasapa limestones, and doubtless the Englewood is also included, 

 but the upper limits of rocks of Mississippian age in both uplifts has 

 not yet been ascertained. 



Along the Laramie range the apparent absence of Lower Carboniferous 

 is an interesting feature, indicating either non-deposition or removal by 

 the very profound later Carboniferous erosion. A short distance east- 

 ward, in the Hartville uplift, there are comprised in the Mississippian 

 the Guernsey formation, 150 feet or more in thickness, and the lower 

 members of the Hartville formation, the two formations being separated 

 by strongly marked erosional unconformity. The basal sediments of 

 the Hartville formation are red sands, and there is strong suggestion that 

 these are of the same age as the red shale at the base of the Minnelusa 

 formation of the Black hills and base of the Amsden formation in the 

 Bighorns. The representative of the Lower Carboniferous in Colorado 

 appears in the small areas at Perry park, about Manitou, about Canyon 

 City, and southwest of Pueblo, and is known as the Millsap limestone. 

 This limestone lies unconformably on the Cambrian, Ordovician, and 

 pre-Cambrian, and is unconformably overlain by the Fountain or 

 lower Wyoming formation, which overlaps directly on the granites in 

 most portions of the area. Its fauna is regarded as moderately early 

 Mississippian. 



UPPER CARBONIFEROUS AND RED BEDS 



The classification of the formations representing later Carboniferous 

 to Triassac time in this region is one of its most interesting problems. 

 Upper Carboniferous and Permian fossils occur at several localities, but 

 some of the sediments have yielded either no organic remains or fossils 

 that do not afford satisfactory evidence as to age. The stratigraphy 

 presents much diversity in different portions of the region, but by ex- 

 tended field work it has been found possible to correlate most of the 

 rocks in the various uplifts. More or less of the Red beds, especially 

 their upper members, have generally been classed in the Triassic, but 

 there is no definite proof whether a representative of this period is pres- 

 ent or not. The fossils which I discovered in 1901 in the upper lime- 

 stones of the Red beds on the east slope of the Big Horns are thought 

 to be Permian, but possibly they may be Triassic. The fossils of the 

 southern Kansas-Oklahoma upper Red beds are regarded as Permian, 



