194 Wisconsin Academy of Sciences , Arts and Letters . 
were found at any point.* Beds which I refer to the Laramie were first 
seen on Dry Fork, a branch of the Marias Liver, and they were traced 
from there all the way to the 49th parallel. On the Two Medicine, near 
the Mission, the supposed Laramie has been cut through by the stream 
and black shales of presumably Cretaceous age are exposed. The Lara¬ 
mie has a thickness here of about 500 feet. In most of the exposures 
seen it has a greenish color and the beds consist of an intimate admix¬ 
ture of sand and clay without the usual seams of lignite and with fewer 
concretions than are commonly observed in these beds in North Dakota. 
On a branch of Swift Current, near St. Mary’s Lakes, the Laramie was 
again seen close up to the base of the mountains, underlain by soft 
black shale, which appears to be Benton. No tertiary beds were seen 
although they may exist here. The beds later than Laramie were small 
local fluviatile deposits still in process of formation. 
The foot-hills. — The rocks exposed in the foot-hills seem to be largely 
of Cretaceous age, though there are some beds of limestone that can 
hardly be so young as Cretaceous. 
Structure of the mountains .— I have already ref erred to the precipitous 
character of the east base of the mountains.4 This appearance is due 
to the structure of this portion of the mountains. A fairly correct idea 
of this structure may be obtained by imagining a long fold to be frac¬ 
tured along the anticlinal axis, and the eastern half to fall back to nearly 
its original position, leaving the western half of the fold to stand at its 
elevated position. The plane of fracture thus becomes the eastern 
escarpment of the mountains and the foot-hills are the disturbed edges 
of the upper strata of the down-sinking eastern half of the original fold. 
I suppose it is altogether more probable that the eastern half never rose 
at all, but that the faulting was accomplished by the simple elevation of 
the western half. The effect is the same in either case. It will be under¬ 
stood I presume that the uplifted western portion does not present an 
unbroken wall for hundreds of miles as might perhaps be inferred from 
what I have said. I have spoken of a single fault; in reality there are 
several, roughly parallel to each other and less so with the general trend 
of the range. There have also been transverse fractures, or else the 
streams have done valiant work in cutting through the rocky walls in 
which their beds are made. The total result of all the forces at work 
* At Fort Shaw the Sun River runs over shales containing fossil Inocerami, beautifully 
preserved. 
+ Captain Twining, of the Boundary Commission, speaking of this region, says: “ I had 
been led to suppose that the ascent to the summit was a gradual slope, and was greatly 
surprised to find that the rolling prairie abutted abruptly against an impassable escarp¬ 
ment of rocky precipices, ft was found to be impossible to carry a continuous line even so 
far as the crossing of the Belly River, and the three stations at this point are connected by 
traverses; the connections between the two final stations are made by a traverse of thirty- 
five miles through the South Kootanie Pass.” Report of Chief Astronomer, p. 65. 
