416 barrell: movements of the strand line 



Turning attention next to the other side of the rhythm of 

 movement, that of the record of submergences, we are led to 

 the conclusion that the emergent phases of the oscillations are 

 relatively rapid and brief, the submergent phase prolonged, and 

 marked by a slowly rising level of the sea. 



The combination of evidence from Maryland and New Jersey 

 suggests strongly that certain early Pleistocene stages of cold 

 climate and glaciation occurred when the ocean level stood at 

 the higher parts of the phases of cyclic oscillation. The impor- 

 tant point is that the development of the cold climates culminat- 

 ing in glaciation does not appear to have required a low level 

 of the sea or high elevation of the land of this region. The 

 evidence of the region marginal to glaciation leans toward the 

 view that the amount of water abstracted for the formation of 

 the ice-sheets was not a major factor in the control of Pleistocene 

 sea levels. It would seem necessarily to have been an impor- 

 tant factor, but the diastrophic rhythm continuing with acceler- 

 ated movement from the Pliocene constituted apparently a 

 factor of more control. 



Post-glacial emergent cycle marginal to the glaciated areas. A 

 third line of investigation is that connected with the Strength 

 of the Crust, a subject now in progress of publication in the 

 Journal of Geology. If the hypothesis set forth there is valid — 

 that a thick and strong lithosphere rests upon a thick zone of 

 comparative weakness, an asthenosphere — then the weight of 

 a continental ice-sheet should tend to depress the crust into this 

 weak zone. As this subcrustal zone is not a fluid it can not trans- 

 miit the excess pressures to unlimited distances. Broad and low 

 pressure ridges would therefore tend to be raised beyond the 

 limits of the ice-sheets. With removal of the ice-load the 

 pressure ridges might rise at first with the central part and then 

 subside. 



This theory has been applied to the data regarding water 

 levels during the retreat of the ice, as given by Woodworth for 

 the Champlain and Hudson valleys.^ The data permit the 



•* New York State Education Department, Bull, 84. 1905. 



