THE CHAMPLAIN SEA IN THE LAKE ONTARIO BASIN 553 



The philosophy of diastrophism is not sharply enough defined 

 to permit an a priori answer to this question. On the one hand 

 are many data, such as those obtained by Michelson 1 in his study 

 of tides, which indicate quick response to external strain; on the 

 other hand are just as many, if not more, facts, such as those con- 

 cerning periodicity of orogenic episodes, which indicate the ability 

 of the earth to delay adjustment for some time after strains begin to 

 accumulate. 



Field evidence in the Great Lakes region strongly suggests con- 

 siderable lag of continental uplift behind ice removal. Post- 

 glacial marine fossils in the Hudson's Bay drainage basin occur at 

 elevations at least as great as 450 feet 2 and indicate uplift of that 

 amount since the Labradorian ice sheet shrank to a diameter of 

 less than two or three hundred miles. The highest shore line of the 

 Champlain Sea rises toward the north at an average gradient of 

 more than 2§ feet per mile and is essentially parallel to the Iroquois 

 strand — sufficient proof in itself that the uplift of the St. Lawrence 

 region, in greater part at least, lagged considerably after removal of 

 the ice load. 



The facts concerning Quaternary diastrophism in the region 

 covered by the Labradorian ice sheet seem to be in complete agree- 

 ment with the conclusion reached from field evidence in Napanee 

 Valley, namely, that the late Wisconsin and Recent uplift did not 

 cause the marine strand to retreat until after an appreciable interval 

 of sea-advance had resulted from the melting of the ice. 3 



1 A. A. Michelson, "Preliminary Results of Measurements of the Rigidity of the 

 Earth," Jour. Geol., XXII (1914), 97-130. 



2 A. P. Coleman, "Lake Ojibway; Last of the Great Glacial Lakes," Ontario Bur. 

 Mines, Ann. Rep., XVIII (1909), 284-93. 



3 In determining the amount of deformation affecting the shore lines of an inclosed 

 body of water, such as Lake Iroquois, during its existence, the distortion of its surface 

 by gravitative attraction should by no means be disregarded. Retreat of the ice 

 front will, in effect, carry the inclined plane of the water surface northward and at the 

 same time cause it to approach more closely a horizontal position. The result will be 

 splitting of beaches north of the lake's outlet, and drowning of the older shore features 

 south of the outlet. This apparent, though not real, warping of the basin was in many 

 cases of sufficient amount to be of quantitative importance. One reason why the 

 Nipissing beach, although tilted, departs but little from a true plane, while the Algon- 

 quin and earlier beaches are warped as well as tilted, is that Lake Nipissing was not 

 a marginal glacial lake, as were its predecessors. 



