412 N. H. DARTON STRATIGRAPHY OF THE BLACK HILLS, ETC. 



stone concretions of this upper zone weather out in characteristic tepee- 

 shaped forms which have been designated "Tepee buttes." 



The Pierre shale is overlain by the Fox Hills and Laramie sandstones, 

 which extend far to the north and west in the great basin lying between 

 the Black Hills and the Bighorn mountains. 



Rocky Mountain Front Range in Colorado 

 introductory 



The sedimentary rocks are steeply upturned along the Rocky moun- 

 tains, presenting extensive exposures along the foothill ridges. They 

 have been described by various writers in the reports of the Haydeii 

 survey, in the monograph on the Denver basin, in folios of the U. S. 

 Geological Survey, and in other publications. 



During the past two years I have examined the greater part of the dis- 

 trict with a view of determining details which have not been set forth 

 by previous observers, and especially to correlate some of the strata in 

 their extension from one portion of the district to another. The special 

 features to which consideration was given were the stratigraphic rela- 

 tions of the Red beds in their extension southward from Wyoming, and 

 especially to ascertain whether or not the upper gypsiferous series in- 

 cludes a representative of the Minnekahta limestone and is underlain 

 by the Tensleep sandstone as in the region northward. Another matter 

 of importance was the investigation of the manner in which the lower Red 

 beds are related to the Upper Carboniferous limestones of the southern 

 Wyoming region, and I was interested to trace northward the subdi^ 

 visions of the Benton group established by Mr G. K. Gilbert in the 

 Arkansas Valley region. Attention also was given to the manner in 

 which the marine Jurassic terminated in northern Colorado. All these 



inquiries yielded results which I believe throw light on the stratigraphy. 



• 



FORMATIONS OF THE FRONT RANGE 



Iii the following table is given a list of the formations recognized in 

 the Front range, and in plates 23, 35, and 36 some of the regional varia^ 

 tions are shown : 



