Along the western border of Lake Agassiz here and northward
into Manitoba extends a prominent wooded bluff, the escarpment of
a treeless plateau which from its crest stretches with slow ascent
westward. This escarpment commonly called the Pembina Moun-
tain, is a very marked feature in the topography for about seven-
ty-five miles. It is caused by the outcrop, mostly overspread by
glacial drift, of a continuous belt of nearly horizontal Cretaceous
shale several hundred feet thick. Its le coincides nearly with



STATE OF NORTH DAKOTA 129

the west line of Gardar and Thingvalla townships. Thence it
continues in an almost straight course, a few degrees west of north,
to the international boundary, 'beyond which it runs north-northwest
nearly fifty miles to the vicinity of Treherne. The base of the as-
cent is about 1,225 feet above sea level, and its crest approximately
1,500 feet, northward to the Pembina river, beyond which the base
sinks to 1,150 and 1,100 feet and the crest to 1,400 and 1,300 feet.
The width occupied by the slope varies from a quarter to a half
of a mile.
The natural surface at the quarter-section stake on the north
side of section 32, Thingvalla township, is 1,178 feet above the sea.
Sections 32, 29 and 20 of this township are mostly till, smoothed
by. this glacial lake, the depressions having been filled by leveling
down the higher portions, where many boulders partially embedded
testify to considerable erosion. A broad beach of sand and fine
gravel three to five feet high extends from south to north through
the center of section 29, its crest being at 1,180 to 1,182 feet high.
