516 PLEISTOCENE OF INDIANA AND MICHIGAN. 



tendency to parallel the Azoic boundary. Near this boundary, however, as pointed out some 

 years ago by Chalmers, 1 the northward rise abruptly increases. Whether this is merely an 

 expression of differential effects of elasticity or of slight effects of overthrusting or underthrust- 

 ing or of some other cause has not been determined. The existence of this increased rise has 

 recently been verified by Goldthwait, Johnston, and the writer near Kirkfield and Orillia, 

 Ontario, 2 and by Mr. Leverett on St. Joseph Island. 3 



EUSTATIC AND OSCILLATORY MOVEMENTS. 



Eustatic and oscillatory movements, such as have been described by Suess, are of little im- 

 port in the present discussion, for neither principle appears to have acted perceptibly in the 

 Great Lakes region. The land in the area of horizontality appears- to have been a "steady 

 mass," remaining unmoved throughout the elevation of the lands to the north. It is not im- 

 probable, however, that both of these kinds of deformation have been operative to a slight 

 but recognizable degree along the borders of the continent, where the shore lines of the sea were 

 involved. If such effects have operated there they must also have acted in the region of the 

 Great Lakes at the same time and in the same direction, but they appear to have been too small 

 in amount to be detected. 



TECTONIC EARTH MOVEMENTS. 



WIDE RANGE OF PHENOMENA. 



Although the hypothesis of resilience following depression by ice weight appears to have 

 much strength, perhaps this strength seems greater than it really is, because the phenomena 

 contemplated are confined to a somewhat restricted field. Beyond the region of the Great Lakes 

 a vast stretch of the earth's surface, comprising almost the whole of northeastern North America, 

 including Hudson Bay and all the lands for 400 to 500 miles around it and reaching from New 

 England and Labrador on the southeast to the Arctic Ocean and Bering Sea on the northwest, 

 was affected at the same time and in the same way as the Great Lakes region. The very vast- 

 ness of this area operates to exclude certain hypotheses that have been suggested. The limita- 

 tions which it imposes seem particularly applicable to all hypotheses that depend on the 

 transfer of subcrustal molten magmas, unless the modern conception of an essentially solid, 

 rigid interior for the earth is wrong, and the old idea of a molten, highly fluid, essentially non- 

 viscous interior, moving under hydrostatic laws, is right. The writer is disposed to accept the 

 newer view. But this would exclude the transfer of molten magmas as a cause of resilience and 

 place the whole burden on elasticity, which is calculated to account at most for less than two- 

 fifths of the total uplift. Moreover, the failure of the uplifts to act instantaneously or pari 

 passu with the removal of ice weight casts a further doubt upon the relation of the uplifts to 

 elasticity. 



In the present unsettled state of knowledge concerning the ultimate fundamental principles 

 of geology, and especially of the primary forces involved in dynamic geology, it is not possible 

 to specify with certainty how and in what particular manner the old shore lines may have been 

 deformed by geotectonic processes. Geologists have so long been accustomed to speak of 

 "upheavals" and "subsidences," without having any definite or adequate conception of the 

 cause of such movements, except so far as based on vague ideas of cooling and contraction of a 

 molten globe, that explanations by the use of these terms are indefinite and of comparatively 

 little value. Even now there is no generally accepted explanation of the growth or formation 

 of continents by dynamic processes, and hence there is no genetic classification of the charac- 

 teristic features of continents. Substantial progress along the lines of any contraction hypothe- 

 sis seems unlikely, and real progress seems more likely, at least in the opinion of the writer, 

 along two or three of the newer lines of thought, probably by a combination and modification 



i Chalmers, R., The geomorphic origin and development of the raised shore lines of the St. Lawrence Valley and Great Lakes: Am. Jour. Sci., 

 4th ser., vol. 18, 1904, p. 175. 



2 Summary Rept. Canadian Geol. Survey for 1909, 1910, p. 104. 



3 Personal communication, 1912. 



