PALEONTOLOGICAL GEOLOGY 
71 
With this ponderous pre-Eocene succession of Tertiary sedi¬ 
ments delimited the determination of the full depositional equiv¬ 
alent of the basal hiatus displayed elsewhere becomes one of the 
problems of prime import. For this part of the general rock- 
column the geological record is unusually complete. This is, of 
course, what makes the Rocky Mountain Tertiaries so supremely 
interesting at the present time. It is the diastrophic aspects of the 
problem which demand first consideration. 
When, then, there appears an intercalation of marine beds 
carrying Cretacic fossils, as represented by the Cannonball for¬ 
mation of the Black Hills region, the time element finds closer 
and closer adjustment. In the region to the west the entire 
Cretacic section is in some places removed before the laying 
down of the pre-Eocene deposits. Marine sediments with re¬ 
mains of Cretacic types of life may therefore, easily exist amongst 
fresh-water or epirotic deposits that occur above the unconformity 
plane which marks the great epeirogenic movement which initi¬ 
ated the Tertiary time in the region. 
One feature which does much to confuse Cretaco-Tertiary strat¬ 
igraphy in the Rocky Mountain province is the lithologic similarity 
and presence of coal beds. All such are commonly referred to 
the Laramie formation. In the Mesa de Maya district of north¬ 
eastern New Mexico, for example, the coal-bearing section called 
Laramie is 4000 feet thick, yet we now know that not a single 
foot of it is of that age. The lower half of this section is Mon¬ 
tanan, the midway unconformity represents the span of the 
Laramian, and the upper half is Ratonan or Tertiary. It is a 
section identical with that of the Lance-Union sequence of the 
Black Hills, except that there is no marine member present. 
Keyks. 
I 
Or biaxial Relationships of Lance Series of Montana. In our 
general scheme of taxonomy of geological formations the sea 
gives us our continuous record which diastrophic oscillation di¬ 
vides into various groupings of episodes according to the ampli¬ 
tude and expanse of the crustal movements. Thus is made possi¬ 
ble a classification of rock terranes that has a strictly physical 
basis and that is entirely independent of any biotic or mineralogic 
features which the formations may possess. The advantages 
