Tertiary <m<l Quaternary Baseleveling. — Upham. 241 
conspicuous Pembina mountain escarpment of Cretaceous 
shales, overspread bjr drift, on the west side of this valley, 
deep wells penetrating through the drift to Cretaceous beds 
and older strata along the low valley plain, and the topograph- 
ic features of the land rising eastward from it with nearly the 
same rate of ascent as. on the west, lead to the belief that 
the eastern like the western border of this wide valley is 
formed by an escarpment of Cretaceous shales beneath the 
drift. The baseleveled plain of the Tertiary era has been 
broadly and deeply channeled during a later time of high 
continental uplift, contemporaneously with the erosion of 
canyons in the western and southwestern United States, and 
with the excavation of the lower Mississippi valley, of the 
Delaware and Chesapeake bays, and of other estuaries on our 
southern Atlantic coast. 
Outlying remnants of Cretaceous formations east of the 
Manitoba and Pembina escarpment. 
Although no Cretaceous beds have been reported on the 
north side of the international boundary east of the Manitoba 
escarpment, it may be expected that their remnants will yet be 
found in central and eastern Manitoba. Southward in central 
and southern Minnesota, frequent Cretaceous outcrops are 
known, and in numerous places deep wells, after passing 
through the thick covering of glacial drift, encounter Creta- 
ceous shales and sandstone, which in some instances are found 
to reach to a thickness of several hundred feet. Further evi- 
dence of the eastward extent of Cretaceous formations in this 
state is afforded in its northern part by Mr. II. V . Wine-hell's 
discovery of Cretaceous shales in place on the Little fork of 
the Rainy river* and on the high Mesabi iron range. f Lignite 
fragments, probably derived from the erosion of Cretaceous 
strata, are also occasionally found in the glacial drift upon 
the country south of the Lake of the Woods and between 
Rainy lake and Vermilion lake. Next beneath the drift, a 
considerable depth of Cretaceous beds probably still exists 
upon the greater part of the western two-thirds of Minnesota. 
*Geol. and Nat. Hist. Survej of Minnesota, Sixteenth Annual Report, 
lor 1887, pp. 103-9, 131, 134. 
fA.\i. Geologist, vol. xn, pp. 220-223, on.. 1893. 
