78 REPORT UNITED STATES GEOLOGICAL SURVEY. 



bers are more developed and augmented farther south. While the Lar- 

 amie beds are found on the west slope of the hogback to the north, 

 they gradually reach to the summit of the ridge which they form on 

 Station 4, at an elevation of 9,311 feet. From there on they continue on 

 the crest of the ridge, participating in the various dips as exhibited by 

 the older underlying strata. Near Eifle Creek they stand on edge, but 

 soon dip more gently, conformably with the Fox Hills underneath. In- 

 dications of coal were observed here in the interstrata of dark shales, but 

 at no point were well-developed beds found. North of the agency coal- 

 beds have been found in the same formation, reaching a thickness of 

 about 4 feet. They are located at the southern entrance of Yellow 

 jacket Pass, and have been prospected. 



Within our district Laramie strata occur but once more besides at the 

 Hogback, at the same locality where we find the younger Cretaceous 

 beds. South of Station 40 they form a series of low bluffs, the strata 

 of which dip to the southward. There, too, coal was observed, but its 

 quality was not sufficiently good to admit of its use as fuel. It was 

 very "slaty," having a large admixture of shales and marls within the 

 coal-beds. It is quite possible, however, that this is but a local feature, 

 and that good coal, answering all requirements, may still be found in 

 some region where the Laramie Group is exposed. As is the case with 

 the older groups, we find that the steep westerly dip shown along the 

 hogback ridge soon allows the strata belonging to this formation to 

 drop out of sight. They are hidden from sight under the succeeding 

 Tertiary beds, and do not again appear within our district. Though but 

 a comparatively short vertical distance removed from the Tertiary beds 

 that compose the remainder of the area, the extreme regularity of dip 

 shown by the latter excludes the probability of their being exposed in 

 any other than the quoted regions of our district. 



TERTIARY. 



Groups belonging to this formation extend over by far the greatest 

 portion of our district. More than 3,000 square miles are covered by 

 them. Eesting conformably upon the beds of the Laramie Group, they 

 extend westward to the border of the area surveyed in one unbroken 

 mass. In previous pages the structure of the Book Cliffs has been re- 

 marked upon. The cliffs proper are no more than the steep southern 

 face of a high plateau which has a gentle slope to the northward. 

 Their eastern border may be said to begin where the slope of the Grand 

 Hogback ends. Occupying, as it were, a neutral position, the strata 

 composing this plateau have been subjected neither to the disturbances 

 emanating from the Uinta Group, nor have those from the Elk Moun- 

 tains had any appreciable effect upon them. Thus it occurs that the 

 strata are found in a position which is varied from the normal only in 

 so far as they have been subjected to a rise in the southern or a sub- 

 sidence in the northern portion. They cover all those groups and 

 formations that we have seen pass under them west of the Hogback 

 Eidge. 



Two divisions only of the Tertiary are found within the borders of 

 our district, the Wasatch and the Green Eiver Groups. Of these, the 

 latter has been divided into two subgroups by Powell — into the lower 

 and the upper. I am unable to see the.necessity for such division, al- 

 though it would be a welcome one, so far as the appearance of a geo- 

 logical map of that section of country is concerned. A change takes 

 place in the lithological composition of the strata, but I do not re- 



