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exist on a lower horizon than this, and in beds showing a more decided 
‘ approximation to marine deposiiion, and cretaceous forms of life; in 
of which case their out-crop would occcur still further to the east. It is 
a not, however, very probable that this is the case, as the investigations of 
4 Hayden and others south of the Line seem to show that in the easte rm aa 
— 
= 
‘a region the deposition of lignite did not commence till the conditions coe oe 
a the Cretaceous formation had distinctly passed away. a a , 
a 368, I am now aware of the existence of a lignite bed a few sich ti 
| in thickness. in clay beds underlying the Roche Percée sandstone, ina 
zB tributary of the Souris River, and this, taken in connection with the posi-— 
tion of the presumed representatives of these sandstones in the western 
development of the formation, would seem to show that some thickness — 
of Tertiary beds may underlie them. This would place the outcrop of 
the eastern edge of the formation at least several miles further eastward 
than above stated; as shown in the map accompanying this Report. 
North-westward from its intersection with the forty-ninth parallel, the 
’ position of the line of junction laid down on the map, is not founded on 
direct observation, the country being thickly covered with drift, but 
i includes all known exposures of the Tertiary—joining with Prof. Bell’s 
observations northward—and is probably not in any part of its course far_ 
from the truth. | 
% 369. The paleontological resemblance of the portion of the Lignite 
Tertiary above described, with the typical Fort Union beds, is exact. 
Their lithological similarity, though less to be depended on, is not less — 
striking; but the rocks of the forty-ninth parallel, when compared with 
the sections on the Missouri River, appear to show a general tendency of 
the beds, northward, to include more carbonaceous matter. The lignites 
are more frequently found, are generally thicker, and almost always more 
compact and purer than those of the eastern extension of the Tertiary to 
% the south. The identity of the rocks on the Line, however, from the 
Roche Percée westward to Wood Mountain, with the eastern fresh-water — 
extension of the southern Lignite Tertiary, generally known as the Fort 
Union Tertiary, does not admit of doubt, and to whatever horizon the 
one is finally adjudicated, the other must follow. 
370. In continuing a review of the formation westward, the sections 
in the Bad Lands south of Wood Mountain next require mention. Here 
the Lignite Tertiary is found with a somewhat different appearance ; 
and westward from this point it gradually changes, till in the region 
around the Buttes, it has assumed an appearance so entirely different 
Be 
