HELL CREEK BEDS, CERATOPS BEDS AND EQUIVALENTS 209 



The vertebrates and invertebrates found in the typical " Ceratops 

 beds" will be considered later. 



16. AREA TO THE EASTWARD OF THE BIGHORN MOUNTAINS, WYOMING. 



To the northwest of Converse and Weston counties, Wyoming, 

 the beds under consideration occupy a vast area in the central Great 

 Plains region between the Black Hills and the Bighorn Mountains, 

 extending into Montana for an unknown distance, and completely 

 encircling the Bighorn Basin. The complete areal distribution in 

 this region is not yet a matter of published record, though the pres- 

 ence of the beds at numerous points is attested. Mr. N. H. Darton^^ 

 to whom we are indebted for most of the published knowledge con- 

 cerning this area, made the following disposition of the Upper Cre- 

 taceous and Tertiary rocks of the region. The name of Parkman 

 sandstone was given to the several hundred (about 350) feet of soft 

 sandstone overlying the more typical Pierre shale, which, from its 

 position, was supposed to represent the Fox Hills, but according 

 to Dr. T. W. Stanton it may be as old as the Claggett — one of the 

 lower members of the Pierre. Immediately above the Parkman 

 but separated from it with difficulty, is the Piney formation, a name 

 proposed 



for the lowest formation of the thick series of fresh-water sandstones 

 and shales of later Cretaceous age, formerly designated 'Laramie,' 

 lying in the great Basin adjoining the Bighorn uplift. 



The maximum thickness of the Piney, according to Darton, is about 

 3000 feet, but according to Mr. C. A. Fisher this does not constitute 

 a lithologic unit, only the lower 600 to 800 feet of sandstones being 

 properly referable to this formation, while the remainder, composed 

 of gray sandstones, dark shales and coal streaks, belongs to the lower 

 Fort Union (somber beds). Whatever its proper limits, so far as 

 present facts indicate, the whole section above the marine Creta- 

 ceous is to be regarded as belonging to the Fort Union. 



Unconformably overlying the Piney as defined by Darton, but 

 probably without the intervention of any considerable erosional 

 interval, is a great thickness of conglomerate to which the name 



" Geol. Bighorn Mts., U. S. Geol. Prof. Paper, No. 51, 1906. 



