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CRETACEOUS AND TERTIARY—GENERAL ARRANGEMENT. 153 
366. The upper beds of the Souris River sections, in the vicinity of 
Wood End Depét, though probably occupying a position inferior to those 
of the localities above mentioned, cannot be separated from them by any 
determinate character. They show perhaps a somewhat more regular 
deposition, and a more rapid alternation of conditions, but are little, if at 
all, more indurated. The lower beds of the Souris River sections, including 
the nodular sandstone of the Roche Percée series, are in great part 
arenaceous, which, together with the frequency with which some of the 
molluscs have sustained fracture of their shells during life, would 
indicate disturbed waters. Nothing of the nature of a conglomerate, 
however, occurs, nor can the sandstones often be considered coarse. In 
beds overlying the Roche Percée sandstones, the only remains indicative 
of brackish-water,—being shells of Corbula,—were found; and these 
were in association with preponderating numbers of purely fresh-water 
forms. . 
367. In my Preliminary Report on the Lignite Tertiary, the follow- 
ing remarks, bearing on the position of its eastern limit on the Boundary, 
- were made :—The Souris Valley, for about four miles east of the Roche 
Percée, continues to show numerous sections of the usual clays and sands, 
and hardened sandstone beds,—the latter in one place nearly three miles 
east from Roche Percée,—forming a group almost equally picturesque 
with it. Rather hard beds of sand and sandy clay are seen in several 
places to underlie the sandstones, and one of these was found to be filled 
with well-preserved specimens of a peculiar Paludina. About a mile 
further east, the valley changes its character considerably; the banks 
formerly scarped and clayey, are replaced by regular grassy slopes, ‘and, 
though followed for a distance of ten or fifteen miles beyond this point, 
yielded no further sections. This change I am at present disposed, in 
the absence of more certain data, to consider as indicating the passage 
from the Lower Tertiary beds to the Cretaceous. The eastern edge of 
the outcrop of the harder beds connected with the Roche Percée, also 
appears to be indicated by a slight, though pretty well defined step in 
‘the level of the prairie, which may be considered as the first gentle 
rise of the Missouri Coteau, and runs about south-eastward to the 
Boundary-line, which it crosses near the 240 mile point. The spring, 
known among the Half-breeds as Peter’s Spring, lies at the foot of this 
step, not far north of the Line, and is probably connected with the 
junction of the more permeable sandstone beds with the underlying 
impervious clays. It is possible that lignite coals of importance may 

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