
202 B. N. A. BOUNDARY COMMISSION. 
extends, to be more or less nearly contemporaneous. From these very 
circumstances, the exploration of these beds acquires an additional 
importance, and may yet be found to throw much light not only on 
geological, but on biological classification. 
463. The position of the Lignite-bearing formation as a whole, is in 
fact such, that even allowing the classifactory importance of the included 
Cretaceous forms, an observer beginning his stuty of the beds on their 
eastern margin, and proceeding westward, as Dr. Hayden has done; - 
would be completely justified in placing the whole series, at least down 
to the top of Cretaceous No. 5, in the Tertiary ; while a geologist familiar 
in the first instance with the fossils of the underlying Cretaceous forma-. 
tions, and following the Lignite strata eastward from their appearance in 
the Rocky Mountains, would in all probability include the whole series in 
the upward extension of the Cretaceous, though doubts might begin to 
assail him before he reached the upper, or most eastern beds. 
464. Should it be desirable, however, to draw a line in this region, it 
seems to me from a careful consideration of the facts which have come 
under my own observation, and the evidence adduced from other local- 
ities; that it can only be placed above the sandstones of No. 5. Above 
this zone the characteristic Cretaceous Cephalopoda are found rarely, if 
at all, and here lies the only physical circumstance which can be used 
in the delineation of the formations on amap. From its universality, 
and the prominent effect it sometimes has on the surface of the country, 
it seems particularly well suited for the purpose. It has therefore been 
adopted as representing the summit of the Cretaceous in the maps accom- 
panying this Report, and the beds overlying it have been referred to 
throughout as the Lignite Tertiary. 

