66 
PALEONTOLOGICAL GEOLOGY 
From this conclusion the paleobotanists will, of course, dissent, 
but we have now come to the parting of the ways. Our floral 
brethren will continue to say that the Cenozoic begins with the 
Lance strata, but the dominating faunal evidence of both the 
invertebrates and the vertebrates, backed as it is by the field re¬ 
lations and the assumption of two movements of the Laramide 
revolution, binds invertebrate paleontologists and geologists to¬ 
gether in the conviction that the Lance and the Union beds were 
laid down during Mesozoic times. Schuchert. 
Tertiary Aspects of Lance Beds. The question of the ages 
of the Lance and Union sections is a part of a very much larger 
problem involving a conception of the geologic evolution of the 
whole Rocky Mountain province. More than a score of minor 
formations younger than the great wide-spread Cretacic section 
and older than the Wasatch Eocene beds are to be correlated and 
interpreted. These formations present much varied evidence con¬ 
cerning the history of the Cretacic-Eocene transition epoch. 
The old idea of diastrophism which characterized the transition 
from Cretacic to Eocene times is faulty. The change was gradual 
rather than sudden. Although over a large area Cretacic deposi¬ 
tion was ended the uplifting is epeirogenic in character and sedi¬ 
mentation is prevailingly continental in nature. Under these cir¬ 
cumstances environmental change affecting life is by no means 
abrupt as is often assumed. In general the newer picture of 
Rocky Mountain development after Laramian time gives no basis 
for the belief that dinosaurs and some other Mesozoic land types 
could not have survived into the Eocene. Indeed, some of them 
did exist through the long interval when the entire Cretacic section 
was being removed from over a large part of Colorado and ad¬ 
jacent regions. The Lance formation rests in some places with 
erosional unconformity upon the Cretacic Fox beds. The gap is 
of undetermined extent; it may be large instead of small as is 
sometimes claimed. 
The Cannonball shale which separates the non marine Lance 
beds from the Union section demonstrates temporary return of the 
sea from an unknown and as yet undetermined region, probably 
from the north of the Black Hills area after an absence of con¬ 
siderable duration. 
