ENDLicH.] FOX HILLS GROUP LARAMIE GROUP. 77 



We can claim, therefore, for the highest Cretaceous of the region all 

 those strata from the base up to the post Cretaceous horizon. 



The entire Hogback Kidgeis structurally an extraordinarily interesting 

 occurrence. Continuing from Dr. White's district into ours, it extends 

 unbroken for a distance of more than 50 miles to the Grand River, and 

 crossing that enters Dr. Peale's district. In its general structure, it is 

 entirely uniform. A dip to the westward is prevalent, varying in angle, 

 however, and at whatever high angle it may be found, soon returning 

 to a lower one. Thus the same beds, that but a short distance from the 

 Tertiary'strata, stand on edge, underlie the latter conformably six miles 

 farther west, dipping at an angle of about 4P. These flexures are 

 thoroughly characteristic of the Cretaceous formations of the west ; and 

 we have in this instance one, including at the same time post-Cretaceous, 

 and in part Tertiary strata. The connection and correlation of this ridge 

 with continuations both north and south will furnish a clew to the causes 

 for its existence. 



On the White, nea'r Station 40, we find another outcrop of the Fox 

 Hills Group, in connection with that of the Colorado shales. It is con- 

 formable with the latter, and varies in no particular feature from the 

 group elsewhere, neither in lithological character nor in the arrange- 

 ment of its strata. With this group the occurrence of Cretaceous beds 

 in our district closes. The area occupied by the formation is a very 

 much restricted one, and one showing exceedingly regular stratigraph- 

 ical arrangement. The total area covered by Cretaceous beds within 

 our district amount approximately 200 square miles. This is a very small 

 portion of the entire area only, and in consequence of the comparative 

 simplicity of stratigraphical features, the Cretaceous formation there 

 presents but few localities of special interest. 



POST-CRETACEOUS. 



Laramie Group. — In our district of 1876 it becomes a matter of con- 

 siderable difficulty to draw the boundary-line between the Fox Hills and 

 the succeeding Laramie Group. Both the upper members of the former 

 and the lower ones of the latter are composed of series of sandstones 

 and shales alternating. In both these groups the- sandstones and shales 

 are very similar, so much so that it is almost impossible to draw the 

 line of distinction between the two. The absence of any characteristic 

 fosvsils is to be regretted, but those that were found certainly do not aid 

 in arriving at any definite decision. Professor White informs me that 

 in his district the circumstances are the same, and that he, as well as 

 I myself, is forced to make a more or less arbitrary division be- 

 tween the two groups. After deliberation I have decided to begin the 

 Laramie with a series of light yellowish to white shales, interstratified 

 partly with sandstones of the same color. These are covered by a 

 series of heavy sandstone strata, separated from each other by grey and 

 brownish shales. These are comparatively constant in their occurrence, 

 and are most typically developed in the southern half of the Hogback 

 Eidge. 



The distribution of the beds assignable to this group is very limited. 

 On White River, about fifteen miles below the agency, they first crop 

 out, forming a portion of the bluff's on its south side. From there they 

 continue in a narrow line due south, occurring along the western slope 

 of the Grand Hogback, and below the divide between White and Grand 

 follow the southeasterly bend made by it. The entire horizontal expo- 

 sure of the group comprises but a narrow strip, although its single mem- 



