THE NORTHWARD EXTENSION OF THE PHYSIO- 
GRAPHIC DIVISIONS OF THE UNITED STATES 
|W. N. THAYER 
Consulting Geologist, Cincinnati, Ohio 
PART I 
INTRODUCTION 
Preliminary to a study of the economic bearing of the physiog- 
raphy of North America the writer found it desirable to inquire into 
the extension of the generally recognized physiographic divisions 
of the United States southward into Mexico and northward into 
Canada and Alaska. ‘The results of the study of Mexican physiog- 
raphy were published in the Journal of Geology early in 1916.1 The 
present paper embodies the results of an investigation of the north- 
ward extent of these divisions. 
The plan of this paper is to discuss briefly the physiographic 
divisions of the United States which touch our northern border, 
and to compare with them the adjacent territory north of the 
International Boundary by reference to surface features, boundaries, 
structure, and physiographic history, and by this means to show 
that the divisions of the United States have northern extensions 
that project them far into Canada and in some places into Alaska. 
This paper is avowedly one of correlation, and no effort has been 
made to give detailed descriptions of the Canadian or Alaskan 
areas. Such work must be left to the future, as there are still 
large expanses of territory that have never been fully explored, much 
less studied, with care sufficient to allow an accurate classification 
of surface features or the drawing of permanent boundaries. The 
generalizations advanced in this paper will, of course, be subject 
to change as our knowledge of the north country increases. 
Fenneman’s classification has been used wherever it could be 
adapted to the continental scope of this paper. The writer’s own 
tW.N. Thayer, Jour. Geol., XXIV (1916), 61-94. 
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