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quently, and a few beds of conglomerate are noted. No lignites wer 
a - however, observed in this part of the formation. its ih ie 
y 373. Where next met with, on the St. Mary River, the beds of th 
formation represented, are probably considerably below those ofthe e- 
last localities. They still have much the same general character; and 
greenish, arenaceous clays are conspicuous. They are more consolida ed, 
rs however ; the coal found here differs considerably from the lignites ofa ny 
- of the eastern localities, and the mollusca, though probably estuarine, 
are decidedly salt-water forms. No reptilian remains were form ines e 
this neighbourhood. ite 
374. It would thus appear, that though the general tendency of the — ie ‘ 
Lignite. Tertiary, is toward salt-water conditions westward, and those of J 
fresh-water lakes to the east, that there are important exceptions; and that, — a a 
while brackish-water forms spread eastward in the lower beds, as faras the 
Roche Percée, fresh-water species are scattered westward, nearly to the ae | 
base of the mountains, and sometimes occur in great abundance. A zone oe 
of sandstones appears to be of very constant occurrence in the formation. 
It appears on the Souris River, forming the Roche Percée. In the Bad — 






















i I 9 
was. 
2 



















z Lands it is about 150 feet above the Cretaceous rocks. In the valley of 
by the Milk River, about 200 feet above the base of the section, and in the | 
‘- | region surrounding the Buttes, at several miles from the base of the 
mountains, and therefore, probably several hundred feet up in uaa 
ee Tertiary. The correlation of the sandstones of any one of these western — 
localities, with those of the Roche Percée, might be open to great doubt; 
but from their occurrence so persistently, at a horizon in the formation, 
_ approximately the same, I think that they may be considered as repre- 
senting the Roche Percée, series with some degree of certainty. In the 
Missouri Region, south of the Line, the Lignite formation is assigned a — 
thickness of about 2,000 feet. I have not met with any locality near the — 
forty-ninth parallel, where it might be even approximately determined ; 
; but, assuming the horizontality of the beds, the rise in the general 
Ss surface of the country would give it, in several places, a thickness of at — 
; least 1,000 feet. 
Ls. From the Souris River, westward, the Lignite Tertiary nearly Ss 
{ always occupies high ground, and frequently forms a well-marked plateau, a 
resting on the clays of Cretaceous No. 4. 
375. Though Ihave not yet had an opportunity of comparing the 
fossils, obtained in the western marine and brackish-water beds of the 
Tertiary on the forty-ninth parallel, with those from the Judith 
