TO YELLOWSTONE NATIONAL PARK. 137 
PERIOD OF MOUNTAIN-ELEVATION. 
Much of the country covered by our reconnaissance is, in some respects, a unique one, as may 
be gathered from the remarks previously made. The prairie, deeply gullied, as it is, by the Mis- 
souri and other minor streams, is, in general, of a pretty level character. The strata are horizontal, 
and there is little evidence of any elevation since those Cretaceous beds were laid down. Above 
the prairie, at a number of points, rise ranges of hills of no very great extent, and with an altitude 
averaging about 2,000 feet. They are seen far and near; and, rising blue and misty in the distance, 
from the dry, parched level, they are a most agreeable relief to the otherwise unbroken monotony of 
the landscape. They are important as serving to redeem the country from utter worthlessness, since 
they give rise to numbers of clear, flowing streams. The Judith Mountains, Moccasin, Highwood, 
Snow, Little Belt, and, north of the Missouri, the Little Rocky and Bear’s Paw Mountains, are the most 
prominent of these ranges. 
Rising, as described, from the level prairie, it is to be expected that they would give good sec- 
tions of the rocks which once lay horizontal over the whole of this part of the country. This would 
doubtless be true, could the relations be studied in detail in each case. In fact, however, the exten. 
sive denudation has left only remnants of once extensive formations, so that in a given spot the 
continuity has been much interrupted. Furthermore, the commonly occurring ejection of masses 
of igneous rocks has served as a decidedly disturbing element. 
As to the time when the elevation of our numerous mountain-ridges took place, the evidence, 
where decisive, points to the same conelusion reached elsewhere in the West, which indeed was to 
be expected. The time of elevation followed the close of the Cretaceous era. This is clearly seen 
at the Judith Mountains, where Cretaceous No. 5 has been involved in the general disturbance: 
The saine cannot be questioned for the Little Rocky Mountains. The elevation of the Snow Mount- 
ains and the Little Belt Range embraced Cretaceous deposits; and, though it cannot be positively 
stated that the upper members of the formation came in at these points, this cannot be doubted, in 
view of the evidence. 
The Bridger Mountains are the most interesting and satisfactory. Shey include strata from the 
Primordial to the top of the Cretaceous; all apparently conformable, and all elevated at one time. 
The junction of the Lower Siluriau with the Carboniferous did not appear in that portion of the 
range examined by us. 
At the other points where the Silurian was found, we unfortunately could not observe its rela- 
tions to the overlying Carboniferous. At the Musselshell Cation, the evidence is not conclusive ; 
but the relations seem to imply conformability from the Cretaceous down to the Primordial. At 
Camp Baker, the Primordial stands alone; and we saw no evidence of the Carboniferous following 
it in the sequence of the strata, as would be expected. This fact strongly suggested to us, while on 
the ground, an earlier elevation of the Silurian; but this cannot be regarded as of much weight, in 
view of the fact that the extensive deposits of Miocene Tertiary may well cover up what follows and 
would otherwise be exposed. 
18 Ww 
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