2o6 KNOWLTON 



of accuracy. The entire section of the region, which begins with 

 several hundred feet of soft, bluish shales of the Pierre, up to and 

 including the acknowledged Fort Union, was supposed by Marsh 

 and Hatcher to be one of continuous deposition; that is to say, no 

 actual unconformity had been detected. The Fox Hills, with an 

 estimated thickness of 500 feet, consists of an alternating series of 

 sandstones and shales. The massive sandstones at the top contain 

 numerous large concretions and a rich marine fauna of character- 

 istic Fox Hills species. The line between the Fox Hills and the 

 overlying beds is a difficult one to draw. Hatcher, at first, placing 

 it arbitrarily at a six-inch band of hard sandstones which separates 

 the fossil-bearing Fox Hills sandstone below from the very similar 

 but non-fossiliferous sandstones above. 



Later, however, Hatcher appears to have changed his mind regard- 

 ing the lower limits of the "Ceratops beds," for he says:-^ 



At no place in the Converse County region do the true Ceratops 

 beds, with the remains of horned dinosaurs, rest upon true marine 

 Fox Hills sediments; nor are the Ceratops beds in this region over- 

 lain by strata which could be referred without doubt to the Laramie. 



This point was apparently well taken, for Stanton and 1 found four 

 species of brackish-water invertebrates in clays above a forty-foot bed 

 of massive sandstone over 400 feet above the highest fossiliferous 

 Fox Hills horizon in that particular section. The fact remains, 

 however, that the fossiliferous portion of the "Ceratops beds" is 

 mainly the upper portion, the highest point at which dinosaurs were 

 found, being only 100 to 150 feet below the Fort Union. 



The fossil-bearing members of the "Ceratops beds" consist, as 

 described by Hatcher,^' 



of alternating sandstones, shales, and lignites, with occasional local 

 deposits of limestones and marls. The diderent strata of the 

 series are not always continuous, a stratum of sandstone gi\ing place 

 to one of shales, and vice versa. This is especially true of the upper 

 two-thirds of the beds. This lack of continuity in the different 

 strata has rendered it well nigh impossible to establish any definite 

 horizons in the upper members of the series. 



"Am. Nat., vol. 30, 1896, p. 117. 



*• Am. Jour. Sci. (3), vol. 45, 1893, P- ^37- 



