254 H. L. FAIRCHILD PLEISTOCENE UPLIFT OP NEW YORK 



vexity of the isobases shown in the maps by Goldthwait implies a flat 

 syncline, pitching south. This suggests two centers of uplift, the west- 

 ward of which might be related to the Keewatin ice-body, and somewhat 

 earlier in time than the eastward movement in response to the waning 

 Labradorian ice-sheet. 



There yet remains a question as to the possible uplift of the territory 

 which shows no deformation of the lake shorelines, south of the zero 

 isobases. Either the southern area (1) has not been uplifted at all, or 

 (2) has uplifted equally over a large territory, or (3) some uplifting 

 occurred previous to Lake Maumee. Goldthwait argues for no uplift 

 during the period of time covered by the life of the lakes. 



As the isobases of our map certainly represent the total Pleistocene 

 uplift in the Hudson-Champlain Valley, and when extended westward 

 harmonize with the data of the area of the glacial lakes, it seems probable 

 that our zero line is correct for the post- Wisconsin uplift. Bearing on 

 this problem is the fact that only the thin edge of the Labradorian ice- 

 sheet (Wisconsin glacial epoch) extended much beyond the zero isobase 

 in Ohio, Indiana, and Illinois, and not at all beyond it in Pennsylvania 

 and New Jersey. The depression and uplift of the New York-New Eng- 

 land area was related to the Labradorian ice-body. The movements of 

 the Mississippi territory may have been somewhat affected by the Kee- 

 watin ice-sheet. 



Conclusion and Summary 



The extension of the isobases of the post-Glacial or marine uplift in 

 the Hudson and Connecticut valleys westward across New Jersey and 

 Pennsylvania and over New York and adjacent parts of Canada is found 

 to correctly indicate the total Pleistocene uplift of all the large area. 

 This is shown in the large map, plate 10. 



The marine plane being determined the whole length of the Hudson- 

 Champlain depression, and around the Covey Hill salient to and through 

 the Saint Lawrence Valley, we have a plane of comparison with the plane 

 of Lake Iroquois. The recent fairly accurate measurement of the alti- 

 tudes of the two planes at the critical point, Covey Channel, the second 

 and final outlet of Iroquois, gives the altitude figures as Iroquois, 1,030, 

 and the marine as 740 feet above ocean. 



It is believed and assumed that the time interval between the draining 

 of Iroquois from its Covey outlet and the ingress of the sealevel waters 

 into the Saint Lawrence-Ontario Valley was so short that no considerable 

 land uplift occurred during that episode, and that therefore the vertical 

 distance through which the waters fell, 290 feet, must be approximately 



