322 ANNUAL REPORT SMITHSONIAN" INSTITUTION, 1920. 



mergence by deposition of land detritus in the seas. Doubtless both 

 of these processes contributed to the displacements of the strand 

 line— clastic deposition continuously, and deglaciation more occa- 

 sionally, in effecting submergence; accumulation of glacial ice and 

 submarine deformation in effecting emergence. In all cases the work 

 of these agents tended to produce an even rise or fall of the sea 

 level. So far then as the coast lands are concerned the displacement 

 of the strand line by these two causes would have been essentially 

 eustatic. 



But we know that, commonly at least, the displacement of the 

 strand line was not entirely eustatic but more or less differential 

 even in short distances. Other causes, such as deformation by load- 

 ing, variable gravitational attraction, etc., must have contributed 

 to produce the complex result. Of these other factors, I am sure 

 locally varying movements within the land masses themselves, in- 

 cluding the more or less submerged shelf, are the most important. 

 What the relative effects of the several factors in each particular 

 case may have been constitutes a most difficult and varying problem. 

 These proportions can not possibly have been the same in all cases. 

 Besides only one of the causes of submergence — namely, the filling 

 of the sea basins with deposit — could have been constantly in oper- 

 ation though obviously most variable in the volume of result. Then, 

 on the other hand, either sudden or gradual deepening of an ocean 

 basin would by itself suffice in effecting emergence. 



Up to a certain point I agree with the suggestions of Penck, 

 Daly, and others concerning the competence of the Pleistocene ice 

 sheets to effect considerable lowering of the sea level ; and the evi- 

 dence indicating warping of the land surface, because of the uneven 

 distribution of the ice load, as first pointed out by Jamieson, seems 

 to me reasonably compelling. I believe also that in deglaciation 

 the land surface largely reestablished itself by elastic, or rather, 

 isostatic rebound to preceding relief. 



Though accepting in modified form the idea of glacial control 

 of particularly Pleistocene sea levels, it is not to be denied that 

 the present well-known occurrence in Newfoundland and in re- 

 mote outlying stations along the coast of New England and the 

 Maritime Provinces of many plants characteristic of the coastal 

 plain of New Jersey and the south tends, as expressed by Bar- 

 rell, 2 "to rule out the hypothesis that emergence was controlled 

 only by the level of the ocean water as controlled in turn by gla- 

 ciation." The extraordinary distribution of plants referred to could 

 not be brought about by natural processes to-day. Evidently the 

 northern occurrence of this flora is to be viewed as remnants of a 



2 Amer. Journ. Sci., 40, 17, 1915. 



