Tertiary and Quaternary Baseleveling. — Upham. 285 
ity, periods of glaciation, by relative instabilit} T , of the land 
with reference to the sea. 
Baseleveling of itself is not destructive to land life; both 
glaciation and marine invasion are sterilizing in their effects. 
The theory of the subaerial origin of plains of denudation 
helps our conception of the conditions which have favored the 
continuit} T of land life on the earth : the theory of marine de- 
nudation compels us to adopt for the same time and place the 
conclusion that land life was driven out. The former, newer 
view is in accord with the fact that the fauna and flora of a 
country is more closely related to antecedent fossil forms 
than to exotic life; it is also consistent with the theory that 
the existing continents have long stood as dry lands, though 
temporarily invaded by the sea. 
TERTIARY AND EARLY QUATERNARY BASELEV- 
ELING IN MINNESOTA, MANITOBA, AND 
NORTHWESTWARD.* 
By Warren Upham, Somerville, Mass. 
CONTENTS. Page. 
Baseleveling of the Cretaceous northwestern plains during the Tertiary era 235 
Areal and vertical extent of this Baseleveling 236 
Renewed Elevation and partial Baseleveling at the close of the Tertiary and during 
the early part of the Quaternary era 238 
Origin of the Red river valley and the Manitoba escarpment by this later erosion.. . 240 
Outlying remnants of Cretaceous formations east of the Manitoba and Pembina es- 
carpment 241 
Topographic Features of Minnesota and Manitoba due to these cycles of Baselevel- 
ing 242 
Direction of the Tertiary and early Quaternary drainage 243 
Relationship of the later Baseleveling to the Ice age 244 
Comparative estimates of the Amount of Erosion in this region during Tertiary 
time and during the Lafayette, Glacial, and Recent periods of Quaternary time.. 24."> 
Baseleveling of the Cretaceous northwestern plains dur- 
ing the Tertiary era. 
From the valleys of the Mississippi and Minnesota rivers. 
the Red river of the North, and lake Winnipeg, a broad area 
of plains ascends gradually westward to the foot of the front 
ranges of the Rocky mountains. The first ascent from the 
Minnesota and Red river valleys and from the flat country en- 
closing lakes Winnipeg, Manitoba and Winnipegosis is mainly 
by an abrupt escarpment, eroded in the Cretaceous strata 
*Read before the Geological Societj of America al the Brooklyn meet- 
ing, Ang. l.">. 1894. 
