ORIGIN OF THE GREAT LAKES BASINS 



By Francis P. Shepard 

 University of Illinois 



INTRODUCTION 



The time-honored hypothesis of glacial excavation as the principal 

 cause of the Great Lakes basins appears to have fallen into disrepute. 

 Most of the latest textbooks of geology and physiography either fail 

 to mention a cause for these greatest of the world's fresh-water lakes 

 or state merely that the basins are the product of land warping, 

 glacial erosion, and glacial deposition. A number of writers have 

 questioned the power of ice in continental glaciers to produce deep 

 basins ^ and have given reasons for believing that other factors were 

 more important. However, for one interested in the ice-erosion 

 hypothesis the greatest surprise is to be found in a recent article 

 regarding the bathymetry of Lake Michigan.^ The writer of that 

 paper boldly discussed the origin of the basin without even mentioning 

 the possibility that glacial erosion might have been a factor. It is 

 time that someone challenged this growing neglect of the glacial- 

 erosion hypothesis before it reaches an undeserved state of senility. 

 The present writer became interested in the problem through the 

 study of submarine topography and particularly through comparisons 

 made of the bathymetry of the Great Lakes with that of the conti- 

 nental shelves and inlets in glaciated territory. 



OBJECTIONS TO ICE EROSION 



In regard to the Great Lakes the best statement of the objections 

 of ice erosion is to be found in Thwaites' Outline of Glacial Geology.* 



1 Reprinted by permission from the Jom-nal of Geology, vol. 45, no. 1, January-February 1937. 



> Fairehild, H. L., Ice Erosion Theory a Fallacy, Bull. Qeol. Soc. Amer., vol. 16, pp. 13-74, 1905; Spencer, 

 J. W., Origin of the Basins of the Great Lakes of America, Amer. Geol., vol. 7, pp. 86-97, 1891; Taylor, F. B., 

 Study of Ice-Sheet Erosion and Deposition in the Region of the Great Lakes, Bull. Geol. Soc. Amer., vol. 

 22, p. 727, 1911; Thwaites, F. T., OutHne of Glacial Geology, 1st ed., pp. 42-44, 1927 (2d ed., p. 20, 1934). 

 This excellent treatise on aU phases of glaciatlon provided much information used in preparing the present 

 article. 



» Evans, O. F., Bathymetric Studies of the Lake Michigan Basin, Geog. Rev., vol. 25, pp. 667-671, 1935. 



* Op. cit. The first edition contains a more complete statement, although the second edition is more 

 moderate in its condemnation of glacial erosion. 



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