332 JR. S. Lull — Mammals and Horned Dinosaurs. 



were longitudinally fluted and many feet in length. There 

 were bands of softer clays often at the same level as the sand- 

 stone, but local in extent. This rapid change in the character 

 of the deposition, which has been noted by previous observers, 

 greatly complicates the task of unravelling the stratigraphy, as 

 no two sections taken at different places in the region agree. 



East of Buck Creek the sediments are marine and of Pierre 

 age. Overlying the Pierre is the Fox Hills, again marine, and 

 Stanton had no difficulty in finding the line of demarcation 

 clearly indicated. We were not so fortunate. West of Buck 

 Creek the sediments are still of Fox Hills age and, so far as 

 one can see from the physical evidence, they pass without a 

 break in the deposition into those of the Lance formation. 

 Nor can one tell, except for the contained fossils, to which 

 series the sediments belong, and as there are some 400 feet 

 devoid of fossils, which have at different times been referred 

 to each, the precise limitation of the Fox Hills and Lance has 

 been subject to dispute. 



Knowlton (1909, p. 205) thus describes the area: 



The " Ceratops beds" are very limited in extent, extending 

 about 15 miles from east to west, by 30 from north to south. 

 The beds "are best exposed along the eastern and southern 

 borders of a synclinal basin, and according to Hatcher are 3000 

 feet in thickness, though Dr. T. W. Stanton and myself, when we 

 visited the area in 1896, concluded that they could hardly exceed 

 2000 feet, but as a large portion of the beds are exposed at a low 

 broad angle in a broad flat grassy plain, it is impossible to 

 measure the beds with a great degree 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 con- 

 tain numerous large concretions and a rich marine fauna of char- 

 acteristic 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 

 regarding the lower limits of the ' Ceratops beds,' for lie says : 



' At no place in the Converse [Niobrara] 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 overlain by strata which could be referred 

 without doubt to the Laramie.' This point was apparently well 

 taken, for Stanton and I found four species of brackish-water in- 



