PROCEEDINGS OF THE ACADEMY AND AFFILIATED 



SOCIETIES 



GEOLOGICAL SOCIETY 



339TH MEETING 



The 339th meeting of the Geological Society of Washington was held 

 in the Auditorium of the Cosmos Club on Wednesday evening, Novem- 

 ber 12, 191 9. President E. O. Ulrich presided. The program was 

 as follows: 



Reginald A. Daly: Changes of land and ocean levels. 



Field study of the zones of post-Glacial emergence in the Gulf of St. 

 Lawrence, along the New England coast, and in northwestern Europe 

 has suggested two tentative conclusions bearing on general principles 

 of geology. The first is that a world-wide (eustatic) sinking of ocean 

 level to the extent of 20 to 25 feet seems to have occurred since the 

 Wisconsin stage of the Glacial period. Secondly, certain field observa- 

 tions favor Jamieson's hypothesis that the sinking and rising of the 

 earth's crust, due respectively to glacial loading and to unloading by 

 deglaciation, have been accompanied, again respectively, by synchro- 

 nous rising and sinking in the belt peripheral to the ice-caps ; in other 

 words, that these isostatic adjustments have been accomplished largely 

 through viscous deformation of the earth, rather than by purely elastic 

 deformation of the earth's radii. 



The first suggestion has been strikingly enforced by facts recently 

 ascertained in Florida and in the Samoan Islands, as well as by compila- 

 tion of the published statements regarding "raised" beaches and allied 

 forms along the shores of the United States, the Bahamas, Brazil, the 

 British Isles, Australia, New Zealand, Pacific archipelagoes, and else- 

 where. 



Field evidence for the second suggestion has been secured chiefly on 

 the Maine coast. There the condition of the shore zone emerged in 

 post- Wisconsin time can best be explained by postulating uplift of the 

 continental shelf during the Wisconsin stage, followed by resubsidence 

 during the Recent isostatic rise of the glaciated region of the continent. 

 If these synchronous movements were actually due to isostatic, viscous 

 deformation of the earth's crust, similar movement might be expected 

 in other parts of the belt peripheral to each ice-cap of the Pleistocene 

 period. The corresponding test of the general hypothesis involves 

 questions as to working of the abandoned shore-lines of Lake Passaic 

 and of the Great Lakes; the origin of the submarine "channel" of the 



so 



