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



does not take place at the same horizon throughout, and the Fox Hills 

 fauna appears in connection with the sandy sediments. 



Usually the Fox Hills deposits are less than 300 feet thick, but in the 

 Denver region, where they comprise a thick mass of sandy clays in their 

 lower portion, they attain a thickness of a thousand feet. The top mem- 

 ber in this region is a persistent characteristic sandstone 50 feet thick, 

 which appears to be the same as the Trinidad sandstone in the Spanish 

 Peaks district in southern Colorado. The top of the Fox Hills forma- 

 tion is not always clearly defined, but in most cases the Laramie beds, 

 being the product of shallow and fresh waters, are distinctive in character. 



LARAMIE 



This great series has received no special study in connection with the 

 present investigation, and it has been separated from the adjoining for- 

 mations only in a few localities. The work of Cross in the Denver basin 

 and of Hills in the Spanish Peaks region has shown that it is of less 

 thickness than originally supposed, and the great mass of overlying 

 coarse sediments are of early Tertiary age. The thickness of the forma- 

 tion, as thus delimited, averages about a thousand feet in the Denver 

 region and nearly twice as much in southern Colorado. 



