244 W. N. THAVER 
single view, but none the less real on that account—the difference 
between a surface of morainic ridges and till sheets. The northern 
boundary begins near Fort William, Ontario, and in a general way 
follows the shore line of the Great Lakes to the vicinity of Kingston, 
Ontario, where it closes with the eastern and southern boundary. 
This boundary is placed at the contact of the pre-Cambrian bedrock 
of the Laurentian Plateau and the sediments of the glacial lakes. 
As drawn on the accompanying map it practically coincides with 
the Algonquin-Iroquois beach as mapped by Upham," and Leverett 
and Taylor.’ 
This section has two well-defined types of topography. The 
first consists of lacustrine plains immediately surrounding the 
existing lakes and bounded in places by morainic ridges concentric 
with respect to them. These “lake plains” are built up of the 
sediments of glacial lakes that covered an area greater than the 
present lakes. They are in topography, age, and structure analo- 
gous to the lacustrine plains of the Western Lake region. A narrow 
strip of territory of this type extends around to the Canadian side 
of the Great Lakes. 
The second type of topography embraces areas characterized 
by ground moraine, morainic ridges, swamps, and small lakes. 
These areas border the “lake plains” on the south and constitute 
by far the larger part of the section. Similar topographic features 
are found north of the Great Lakes, in fact, they are widely scattered 
over the Laurentian Plateau, but they are so decidedly subordinate 
to the features of the old erosion surface that no great difficulty is 
experienced in locating the dividing line between the two provinces. 
This second type of topography is particularly well developed in the 
peninsular portion of Ontario. 
Glaciation is of course the main topic to be discussed in the 
physiographic history of this section. All of the principal features 
of the topography are the results either of unequal glacial accumula- 
tion or of the alteration of drainage lines; and although preglacial 
topography probably conditioned results to some extent, it is now 
« Warren Upham, U.S. Geol. Survey, Mon. 55. 
2 Frank Leverett and F. B. Taylor, U.S. Geol. Survey, Mon. 53. 
3 F. B. Taylor, Geol. Survey Canada, Summary Report (1909), pp. 164-67. 
