W. Cross — Post-Laramie Deposits of Colorado. 37 



has not been carefully explored as yet except for vertebrate 

 fossils. And marked angular unconformity at the base of 

 these beds might not be distinguishable if the shore line was 

 too far removed from the localities examined. But even the 

 general statement of Prof. Marsh seems to indicate a great 

 actual unconformity, for he says, in the sentence quoted above, 

 that, in some places not specified, " various older formations 

 are found immediately beneath it " (i. e. the Ceratops horizon, 

 called " the typical Laramie"). As invertebrates and plants 

 are stated to be associated with the vertebrate fauna it seems 

 quite necessary that their testimony, as well as all available 

 strati graphical and lithological details, should be given, before 

 the beds in question can be satisfactorily correlated. 



The cited statement of Prof. Marsh that " the Ceratops beds 

 have now been traced nearly eight hundred miles along the 

 eastern "flanks of the Rocky Mountains" implies the actual 

 connection of the formations of the Denver field with that 

 containing the new fauna in Wyoming. But the area of the 

 Denver beds is known to be quite limited, and the Arapahoe 

 beds on the plains east of Denver are thin and erosion has 

 entirely removed them in many places, exposing the under- 

 lying Laramie. It is, however, possible that they thicken again 

 farther out on the plains, or reappear to the northward beyond 

 the Platte valley. If the investigations of Prof. Marsh have 

 actually connected the Ceratops beds of "Wyoming with the 

 Arapahoe beds of Colorado, this fact is of great importance as 

 fixing the stratigraphical position of the Ceratops horizon as 

 post-Laramie. If, however, the Ceratops beds of Wyoming are 

 contemporary with the true Laramie, then they do not belong 

 to the same epoch as the Denver and Arapahoe beds. 



The above considerations show that the vertebrate fossils of 

 the Arapahoe and Denver beds cannot at present be used as an 

 argument either for or against the proposed separation of 

 these lake-beds and their equivalents from the Laramie, be- 

 cause the new fauna recently described has not been identified, 

 in published statements at least, in strata satisfactorily iden- 

 tified with the true Laramie on other ground than that of the 

 new fossils themselves. . It is clearly suggested by the known 

 evidence that the new family of Dinosaurs may be found to 

 be specially characteristic of the epoch to which the lake-beds 

 described belong, as distinctive from that of the Laramie 

 proper ; that their remarkable specialization may have taken 

 place largely as a result of the changed conditions following 

 the great orographic movement closing the Laramie. Until 

 more is known about the distribution of the Ceratopsidse and 

 their immediate ancestors in the Cretaceous series of forma- 



