LAND AND SEA OSCILLATIONS ULRICH. 325 



the New Jersey part of the coastal plain and extended widely into 

 the eastern valleys of the adjacent Appalachian region. As the ice 

 sheet retreated Maryland settled back while the coast lands to the 

 north rose. The resulting emergence and the reversal of the tilt of 

 the land surface must have produced corresponding changes in the 

 direction of flow of affected rivers. Obviously results like these re- 

 quired practically immediate isostatic response to both the accumu- 

 lation and the removal of the burden of ice and not as Barrell 

 thought, "a deferred intermittent, and possibly oscillatory, read- 

 justment." (Op. cit. p. 21.) On further retreat of the ice front the 

 upward movement of the latter was arrested and finally reversed, 

 so that it shared in the general subsidence of the marginal area when 

 the complete withdrawal of the ice sheet permitted isostatic rebound 

 of the unloaded interior highlands to their preceding and present 

 normal land altitudes. 



In consequence of the bulging of the sea bottom adjacent to shore 

 lines that in the maximum spread of the ice sheets had sunk beneath 

 the load of ice, the capacity of the ocean basin must have been cor- 

 respondingly lessened. This in turn would have tended to retard 

 and finally reverse the downward direction of the change in sea 

 level previously prevailing on account of subtraction of ocean water 

 for the making of the ice sheet. That is, it would have caused actual 

 raising of sea level except in those parts of the shore line that were 

 covered by the ice sheet and therefore directly affected by its weight. 

 The upward movement of the sea level thereby occasioned would 

 have been worldwide and eustatic. 



But the displacements of the Pleistocene strand line along the 

 Atlantic coast that were in any wise connected with glaciation must, 

 because of varying conditions arising from the fact that the ice sheets 

 did not reach the shore line south of New Jersey, have varied greatly 

 in amount and direction at different places. It was only in the early 

 stages of glaciation, before peripheral elevation of the surface of the 

 lithosphere with respect to areas bearing ice loads had progressed 

 to the stage wherein it caused material lessening of capacity of 

 ocean basins, that the sinking of sea level could have been eustatic. 

 On the reversal of this sea-level movement, when the Pleistocene ice 

 sheet stretched to the shore and when as stated above, the consequent 

 bulging of adjacent parts of the continental shelf reduced the capac- 

 ity of the ocean basin, the change in sea level as manifested in the 

 advance and retreat of the Atlantic shore north of, say Cape Hat- 

 teras, was far from eustatic. During this maximum extent of the 

 Labrador ice sheet, the ice-covered near-shore lands about the Gulf 

 of St. Lawrence must have sustained extensive submergence. South- 

 wardly from northern Maine to New Jersey the amount of this sub- 

 mergence decreased perhaps to its minimum. On the other hand, in 



