THE FOSSIL FIELDS OF WYOMING 



Niobrai;a is yellowish white chalky marls and impure limestone. 

 The Fort Pierre consists chiefly of clay beds. The Fox Hills 

 Cretaceous is a coarse argillaceous sandstone. Fish scales 

 occur in the Colorado clay beds. 



f' In Hayden's report, for 1874, he says that a few species 

 of plants probably began their existence in the Fox Hills and 

 continued on up into the Lignitic where they reached their 

 highest development. Remarkable concretionary masses often 

 characterize the upper Fox Hills beds, weathering so as to 

 leave caps at top. The Fox Hills is important in a biologic 

 view, for no animal and but few vegetables pass above. A 

 few plants began in the Fox Hills and continued up into the 

 Laramie. 



King, in 40th Parallel Survey, says that the valleys of Big 

 Laramie, Little Laramie, Dutton and Rock Creeks are eroded 

 through Colorado shales and marls. North of the 4 1 st 

 parallel, the Fort Pierre is the uppermost Cretaceous. South 

 of it, the Fox Hills sandstones form a broad belt extending 

 southwardly beyond the 40th parallel. On Laramie Plains, the 

 Fox Hills lie north and east of the Medicine Bow Range, 

 chiefly on Rock Creek and Mill Creek. South of Mill Creek, 

 the brownish gray sandstones carry carbonaceous shales with 

 seams of coal and impressions of deciduous leaves. On the 

 north side of Cooper Creek are thin seams of lignite. On 

 Cache la Poudre Creek, the Fox Hills attains a thickness of 

 1,200 to 1,500 feet, consistmg of friable sandstone, rendered 

 impure by the presence of clay. From Medicine Bow to Car- 

 bon the Fox Hills forms the surface rock. Near Separation 

 Peak, the Fox Hills Cretaceous may be 3,500 feet thick to 

 4,000 feet south of Fort Steele. Four miles northeast the Fox 



—42— 



