446 proceedings: geological society 



a number of good observers have estimated to be about 1000 meters. 

 Taking this value and assuming the deglaciated area to be equal to 

 one-fifteenth the area of the ocean, or, roughly, twice the glaciated 

 area of North America, we estimate the change in sea-level to have 

 been about 67 meters. As already stated, this is only an estimated 

 change, but perhaps it is a conservative estimate. 



In this connection it is interesting to note that the complete de- 

 glaciation of Greenland and Antarctica, if their ice caps average 1000 

 meters thick, would raise the sea-level about 40 meters, of which Green- 

 land would contribute about 6 and Antarctica 34. Presumably these 

 changes in sea-level which must have occurred as a result of glaciation 

 and deglaciation are best preserved in equatorial regions. The change 

 of load was more evenly distributed here than in the higher latitudes, 

 and therefore local warping was probably much less. 



Discussion: President Woodward of the Carnegie Institution of 

 Washington had been expected to lead the discussion of the papers 

 which had. been presented, but was unable to be present. President 

 Vaughan called upon Dr. William Bowie of the Coast and Geodetic 

 Survey for some remarks. Dr. Bowie said that in his opinion the 

 oscillations of the strand-line spoken of by Professor Barrell, involving 

 movements over large areas, could hardly be accounted for by the 

 theory of isostatic adjustment. Deposition of sediment on ocean 

 floors, continued over long periods of time, would be expected to cause 

 eventually a sinking of the floor on which they rested, and islands which 

 were surrounded by such areas of loading would naturally participate 

 in the downward movement; but a subsequent rise or oscillation of 

 level, such as had frequently been noted, could not be explained by 

 isostasy, and other physical and chemical forces must be invoked. 

 Likewise the unloading of land areas by erosion would be expected to 

 result in upward movements, but oscillations could not be explained 

 as effects of isostatic adjustment. He thought that as regards this 

 question as a whole geodesists should not be expected to advance theo- 

 ries in explanation of the movements which geologists have recognized. 

 The primary purpose of the geodetic work in making measurements of 

 gravity is to determine the shape Of the geoid. The results thus ob- 

 tained give quantitative data which geologists may employ in explaining 

 the phenomena observed. 



J. W. Spencer spoke of the great submergences which he had for- 

 merly believed were shown in the West Indian region. He was now 

 somewhat doubtful about the evidence on this matter, but was more 

 certain regarding the region of the Great Lakes. He had traced 

 several low terraces around Lake Ontario, and their parallelism with 

 the present water-surface showed that the region had undergone no 

 deformation during the time taken by the St. Lawrence River to cut 

 its channel 15-20 feet deeper. He spoke also of the work of D. W. 

 Johnson as tending to establish the lack of recent deformation along the 

 Atlantic Coast. At the same time various observers have found evi- 



