242 The American Geologist. October, 1894 
Concerning their eastern limits, Prof. N. H. Winchell, the 
state geologist, writes: 
A lint' drawn from the wesl end of Hunters' island, on the Canadian 
boundary line, southward to Minneapolis, and thence soutbeastwardly 
through Rochester to the Iowa state line, would, in general, separate 
thai pari of the state iii Which the Cretaceous is noMinown to exisl from 
thai in which it docs, li is not here intended to convey the idea thai 
the whole state wesl of this line is spread over with the Cretaceous, be- 
cause there are many places where the drift lies directly on the Silurian 
or earlier rocks; but throughout this pari of the state the Cretaceous 
exists at least in patches, and perhaps on ce extended continuously.* 
Topographic Features of Minnesota and Manitoba due to 
these Cycles of Baselevelin<;. 
Cretaceous deposits originally overspread all of Minnesota 
and Manitoba, excepting possibly portions of their eastern 
borders. The long Tertiary cycle of baseleveling greatly re- 
duced the thickness of these beds, but their part remaining at 
the end of the Tertiary era appears to have still formed a 
general envelope, with mostly a nearly level surface, above the 
older rocks for a distance of 100 to 200 miles eastward from 
the Manitoba escarpment, the Pembina mountain and the Co- 
teau des Prairies. Occasional tracts of hills, as the Turtle 
mountain, or a great highland ridge, as the Coteau des Prai- 
ries,! rose 500 feet or more above the general level. 
With the ensuing epeirogenic uplift which marked the 
transition from the Tertiary to the Quaternary era, the 
streams again began a vigorous work of erosion. The broad 
Red river valley, with its enclosing escarpments, and the low 
lake district of Manitoba, with the great escarpment on the 
west, then were sculptured to nearly their present forms. 
In various parts of Minnesota, as Langhei and the vicinity 
of Glenwood in Pope county^ conspicuous highland tracts 
and the depressions occupied by lakes seem attributable to the 
contour of the ( 'retaceous beds beneath a somewhat uniform 
mantle of the glacial drift. Another district of similar fea- 
tures is the neighborhood of Pokegama lake on the upper 
.Mississippi and all the country thence westward to lake 
Itasca. The Pokegama lake, with its irregular arms, proba- 
*Bulletins of the Minnesota Academy of Natural Sciences, vol. i. p. 
348. Compare also Geology of Minnesota. Final Report, vols, i and n. 
(^Geology of Minnesota, vol. i. 1884, pp. 593, 601, etc. 
fclbid., vol. ii. 1888, p. 192. 
