302 
have reasoned that, inasmuch as these animals are characteristic of the 
Mesozoic and are not known to occur in the Tertiary of any other region, 
they probably did not exist during any part of the Tertiary of this coun- 
try. And certainly, there is a mass of confirmatory evidence for this con- 
clusion. The plants have appeared to furnish evidence against it; but, 
in view of the discrepancy between Lesquereux’s conclusion and his prem- 
ises, it seems that the paleozoologists were justified in their conservatism. 
Mr. Cross writes (Mon. U. S. Geol. Surv., xxvii, p. 251): 
If the dinosaurs of the Ceratops fauna did actually live in the Laramie 
epoch of Colorado they survived a great orographic movement and its ac- 
companying climatic changes, and continued through the Arapahoe and 
Denver epochs so little modified that Professor Marsh has not detected 
any changes corresponding to the stratigraphic time divisions. 
Since this was written it has been found that the Judith River beds, 
which contain so many dinosaurs, were deposited long before the time of 
the Laramie. We thus have proof that these dinosaurs and many other 
forms of vertebrates survived, without important changes, the orographic 
movement mentioned by Mr. Cross. It seems probable, therefore, that this 
movement was not so widely extended and so long continued as has been 
supposed. Why the dinosaurs died out finally we do not know, any more 
than we know why numerous other vigorous races of animals have per- 
ished from the earth. That the causes were not local is shown by the 
fact that in Europe likewise they became extinct just before the appearance 
of the Cernaysian fauna. It may be regarded as very reprehensible in 
them that they thus permitted themselves to perish before the Eocene 
came on, but we are compelled to believe the record. 
In the preceding pages I have endeavored to show that the deposits 
of the Lance Creek epoch are well separated from those of the Fort Union, 
as indicated by both the fauna and the flora. In ease a biological break is 
required between the Cretaceous and the Tertiary such a break seems to 
be present here. The stratigraphical break appears to be less conspicuous; 
yet unconformities are not absent and the character of the deposits appears 
to be such that there is seldom difficulty in separating the one formation 
from the other. Nevertheless, it seems that accurate correlation demands 
that the line between the Mesozoic and the Cenozoic in that region ought 
to be drawn at least above the Puerco and probably through or above both 
the Torrejon and the Fort Union. The exact position of the parting must 
be settled after further investigations. 
