62 ulrich: major causes or oscillations 



of the Coastal Plain and extended widely into the eastern val- 

 leys of the adjacent Appalachian region. As the ice sheet re- 

 treated 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 required practically immediate isostatic response to 

 both the accumulation and the removal of the burden of ice 

 and not as Barrell thought, "a deferred intermittent, and possi- 

 bly oscillatory, readjustment." (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 sub- 

 sidence of the marginal area when the complete withdrawal of 

 the ice sheet permitted isostatic rebound of the unloaded in- 

 terior highlands to their preceding and present normal land alti- 

 tudes. 



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 capacitv of the ocean basin must have 

 been correspondingly 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 le\el except in those parts 

 of the shore line that were covered by the ice sheet and therefore 

 directly aftected by its weight. The upward movement of the 

 sea level thereby occasioned would have been worldwide and 

 eustatic. 



But the displacements of the Pleistocene strandline along the 

 Atlantic Coast that were in any wise connected with glaciation 

 nmst. 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 



