58 ulrich: major causes of oscillations 



marginal parts of the continents have been subjected repeatedly 

 in recent geologic ages to positive and negative displacements 

 of the strandline; also that the vertical element of these oscilla- 

 tions is not uniform in amount at different places. Considering 

 only the Pleistocene to Recent movements, their differential 

 character at once suggests that these were in no case wholly due 

 to either the alternate storing and unloading of water in the form 

 of ice on the lands or, as Suess and Schuchert have it, to re- 

 treats occasioned by periodic deformation and deepening of 

 oceanic basins and ensuing slow submergence by deposition of 

 land detritus in the seas. Doubtless both of these processes 

 contributed to the displacements of the strandline — clastic 

 deposition continuously, and deglaciation more occasionally, in 

 effecting submergence; accumulation of glacial ice and sub- 

 marine 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 coastlands are concerned 

 the displacement of the strandline by these two causes would 

 have been essentially eustatic. 



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

 strandhne was not entirely eustatic but more or less differential 

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

 loading, variable gravitational attraction, etc., must have con- 

 tributed to produce the complex result. Of these other factors, 

 1 am sure locally varying movements within the land masses 

 themselves, including 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 diffi- 

 cult and varying problem. These proportions can not possi- 

 bly have been the same in all cases. Besides only one of the 

 causes of submergence — namely, the filUng of the sea basins 

 with deposit — could have been constantly in operation 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 



