of the Rocky Mountain region. 461 
C. cytheriformis, which also seems to belong to a group ( Velori- 
tina) peculiar to the Tertiary in Europe. 
But the most surprising fact to me, supposing this to be a Cre- 
taceous formation, is, that we found directly associated with the 
reptilian remains at Black Butte a shell I cannot distinguish from 
respect so far as can be seen, that I have scarcely any doubt of its 
identity with the same. 
occurrence of some vertebrates of Cretaceous affinities at the 
Judith River localities, would certainly strongly favor the conclu- 
Tertiary. 
That the Judith River beds may be Cretaceous, I am, in the 
light of all now known of the geology of this great internal region 
of the continent, rather inclined to believe. But it would take 
very strong evidence to convince me that the higher fresh-water 
Lignite series of the Upper Missouri is more ancient than the 
Lower Eocene. That they are not is certainly strongly indicated, 
not only by the modern affinities of their molluscan remains, but 
also by the state of the preservation of the latter. Indeed, these 
shells of the same, picked up along the shores of the streams. 
The entire flora of this Upper Missouri Lignite group has also 
always been considered, by the highest authorities on that depart- 
ment of paleontology, unquestionably Tertiary. 
