6o 



ulrich: major causes of oscillations 



ried it up to a level where it became unstable and a slow settling 

 back occurred as an after-effect, coincident with the last stages 

 of upwarping over the centers of glacial load. The actual 

 evidence at hand does not decide between these hypotheses. 

 The association with the close of glaciation appears to favor a 

 genetic connection with deglaciation, but, on the other hand, it 

 remains to be demonstrated why the extra-marginal zone should 

 rise together with the region directly glaciated, or that the cycle 

 was restricted to such an extra- marginal zone." 



LABRADOR 



NEW EN6LAND 



COASTAL PLAIN AND 

 CONTINEKTAL SMEUr 



s£^ Lcva. 



S£A L£V£L 



Fig. I . — Generalized profiles of eastern North America in Pleistocene stages, 

 indicating isostatic vertical movements of surface of lithosphere in process of de- 

 glaciation: I, during maximum extent of ice sheet, when the outer part of con- 

 tinental shelf was emerged; 2, when the ice load had retreated from the present 

 coastal str P ; 3, a later stage when the ice sheet had been reduced to the area of 

 Labrador; 4. present relief of land, with submergence of continental shelf. Ap- 

 proximately similar conditions may be supposed to have obtained in the growing 

 stages of the ice sheet. 



That the eastern margin of the continent, south of Labrador, 

 did rise to higher levels than the present during the retreat of 

 at least the last Pleistocene ice sheet seems, with Barrell's in- 

 terpretation of Woodworth's^ data and conclusions regarding 



* N. Y. State Education Department.^Bull. 84: 1905. 



