390 R. A, Dalij—Post-Glacial Warping of 



the other causes had ceased to be important, and it would 

 not be surprising if the third cause is still locally at work. 



The available evidence appears to warrant belief that 

 the deformation of the earth's crust under glacial loads 

 has been chiefly elastic. Assuming the largest probable 

 volume for the marginal bulge around the composite 

 North American ice-cap, computation seems to show the 

 purely elastic deformation to have been from fiYQ to ten 

 times greater than the deformation caused by viscous out- 

 flow. The very recent drowning of the marginal belt 

 would therefore be quite moderate — in the regions here 

 considered probably not surpassing a few tens of meters, 

 even though the marginal bulge may have had a maximum 

 height of 200 meters. 



The testing of this theoretical set of deductions by field 

 observations involves close dating of the submergence 

 so clearly manifest in the coast region southwest of Bos- 

 ton and again along the southern shores of Nova Scotia 

 and Newfoundland. In a case of this kind close dating 

 is notoriously difficult, and the writer has been able to add 

 few objective facts relevant to the date of drowning 

 along the coasts studied in 1920. It is certain that the 

 rise of sea-level is there very recent ; the waves have not 

 yet had time to cut wide benches in the little-resistant 

 glacial drift which mantles most of Nova Scotia *and cer- 

 tain stretches of the sea-front in southern Newfoundland. 



On the other hand, tide-gauge records for eastern 

 Canada, published by Dr. W. Bell Dawson, Superinten- 

 dent of Tidal Surveys (Ottawa, 1917), show no measura- 

 ble sinking of the land at Halifax, Charlottetown, and St. 

 Paul Island (Cabot Strait) during periods of from 6 to 

 18 ye'ars. The New England coast seems to have been 

 sensibly stable for at least one hundred years. Shinier 

 describes proofs of submergence of the coast region at 

 Boston within a period of 3000 years. He writes : "The 

 remnants of the fish-w^eir, excavated on Boylston Street, 

 give evidence of man in the Back Bay region of Boston, 

 probably 2000 to 3000 years ago. He built this weir dur- 

 ing a climatic period as warm as oif the Virginia coast 

 at present, and upon a sinking coast. Since its erection 

 the region has sunk sixteen or eighteen feet and suffered 

 a refrigeration to its present climate.''^ Certain facts 

 suggest the necessity of postulating a recent, negative, 



° H. W. Shimer, Proc. Amer. Acad. Arts and Sciences, vol. 53, p. 462, 1918. 



