184 



THE CERATOPSIA. 



beds, with a fresh-water fauna in large part identical with that at Black Buttes and a flora that also indicates the same 

 horizon, have a much greater thickness. Here again there seems to be no break in a series that has Fort Union plants 

 in its upper member. The abundant occurrence of such a species as Campeloma multilineata throughout all but the lowest 

 portion of the series argues strongly for continuous sedimentation. 



The difficult}' of recognizing unconformities in beds so little disturbed and the possibility that there may be such undis- 

 covered breaks in these two areas is freely admitted, though it does not seem to us probable. From the facts now available 

 it seems most probable that in Converse County and in the Bitter Creek Valley the time representatives of the Denver and 

 Arapahoe beds are undifferentiated portions of a continuous series and can not be separated from the Laramie. The Fort 

 Union beds are apparently distinguishable by means of their flora, and these mark the upper limit of the Laramie in the 

 areas in question. 



The Triceratops skulls from Hell Creek represent species whose position stratigraphically 

 is about the middle of the Converse County series of specimens, which is evidence in favor of 

 considering the former deposits as contemporaneous with the latter. 



Geological sequence of the Ceratopsia. 



a Species rejected by Hatcher because of the fragmentary condition of the type- 



b This form is placed anung the Arapahoe Ceratopsia by Whitman Cross on page 230 of the monograph on the Geology of the Denver Basin 

 ( Mon. U. S. Geol. Survey, vol. 27). It must be a case of mistaken identity (see p. 183 of this monograph), 

 c Also Hell Creek, Montana. 

 d Horizon not recorded. 



e Belly River beds. The Montana and Alberta species were contemporaneous. 

 / From upper beds. 

 s From middle beds. 

 h From lower beds. 



Although the formations above the Fox Hills have been placed in regular sequence in 

 the above table, it may be that the Ceratopsia-bearing strata in Converse County include the 

 equivalents of those near Denver. 



