

CRETACEOUS AND TERTIARY—PEMBINA RIVER. 85 
For about 150 miles, the country is so thickly covered with drift deposits, 
that none of the streams cut through them to the underlaying strata; or, 
if the great valley of the Souris does so, they are concealed by its gently 
sloping and grassy banks. When the rocks underlying the drift are 
again seen, near La Roche Percée, they belong to the overlying Lignite 
Tertiary series. 
198. The section seen at the crossing-place of the Pembina River, 
and given above, is the most instructive, as showing the line of junction 
of two portions of this division of the Cretaceous ; of these, the harder 
beds, highest in the section, form the substratum of the plains for a belt 
at least forty miles wide, and extending westward from the front of 
Pembina Mountain. The lower beds characterized by their different 
lithological character, and the comparative abundance of fish remains; not 
only form the base of the Pembina River section, but are extensively 
developed along the front and foot of Pembina Mountain. 
199. Microscopically examined, the clay-shales of the lower series 
are seen to consist of fine argillaceous matter, with some siliceous grains, 
not much rounded by attrition. No minute organisms are visible, and the 
rock does not effervesce when treated with an acid ; proving the entire 
absence of calcareous matter. The upper and harder clay-shales from 
Pembina River and Long River, show almost exactly the same characters. 
Siliceous particles are more abundant, but of smaller size, and more 
uniform; and no effervescence is caused by acid. Both rocks contain 
small quantities of bituminous or carbonaceous matter. When heated 
they blacken, and that of the lower division sometimes even sustains a 
small flame fora momeént. When the carbonaceous matter is removed 
by urging the heat, a hard mass, with much the texture of biscuit porce- 
lain, and of white, or very light dun-colour remains. Some layers of 
these fine Cretaceous clay-shales would yield excellent material for the 
manufacture of pottery. 
200. These rocks, though so barren paleontologically, are of interest 
from the great area which they must underlie, and the very great rarity 
of their exposures. The upper portion of the Pembina Mountain series, 
must have a thickness of at least 300 feet, and taking into consideration 
the gentle westerly dip which the Cretaceous rocks probably possess 
throughout all this region, and which finally carries them under the Tertiary, 
it may be much more. Of the lower portion, it is impossible to speak 
with certainty, but it is probable that a thicisness exceeding 100 feet was 
seen in the various sections examined. It is not pretended that the 
