LAND UPLIFT AND CHANGE OF OCEAN LEVEL 205 



Eelation of Land Uplift to Ice Eecesston 



This topic has been discussed in a previous paper (82, pages 249-252). 

 It was there argued that the rise in the marginal areas of the glaciated 

 territory could not begin until the ice-front was some distance removed ; 

 tiiat the uplift was by a wave movement; and that the wave did not over- 

 take the retreating ice-margin in the Hudson- Champlain Valley. Later 

 study suggests that possibly the uplift wave did overtake the ice-front 

 at the north boundary of New York; in other words, that there might 

 have been a small amount of land rise beneath the thin edge of the ice- 

 sheet while this lay against Covey Hill. The reasons for this are given 

 in the detailed description of the New York features now awaiting publi- 

 cation. 



Theoretically, it seems possible that while the nucleus of the Labra- 

 dorian ice-cap, relatively small in area and much reduced in thickness, 

 lingered in the cool climate of the Laurentian highland some uplift 

 affected that ice-buried area. Whatever rise of the land took place while 

 it was yet covered with ice would not be recorded by aqueous deposits. 

 This conception suggests that the isobases for the central part of the 

 glaciated region may represent only the later portion of the uplift. The 

 study of this matter is bequeathed to the future. In this paper it is not 

 practicable to consider the geophysical problem of diastrophism as related 

 to glaciation. A recent discussion of the subject by Taylor is to be found 

 in the paper listed as number 80, pages 508-518. 



Change in Ocean Level 



The Pleistocene ice-caps consisted of water withdrawn from the ocean. 

 The total mass of the several ice-sheets represented an enormous volume 

 of water, and if the continental glaciers were contemporary the reduction 

 in the level of the ocean was considerable. Even the Labradorian ice- 

 sheet alone must have changed the sealevel. On northern coasts this low- 

 ering of sealevel was in some small amount counterbalanced by the gravi- 

 tative effect of the ice-caps. When the ice-caps melted, the water was 

 returned to the sea and the original level restored. Estimates have been 

 made to the effect that in the equatorial zone the seas were lowered about 

 200 feet (41, 42). 



Evidently this is a complicated problem, involving many meteorologic, 

 geologic, and geophysical factors; and especially difficult when applied 

 to the. closing stage of the latest North American glaciation, with its 

 elements of uncertainty. Without attempting any serious discussion of 



