LAND AND SEA OSCILLATIONS — ULRICH. 327 



Paleozoic stratigraphy are cited in my Revision in support of this 

 belief, and Barrell, in 1915, expressed himself as favoring the view. 



Now, if we accept this conclusion it certainly does not help the 

 hypothesis of measurable sea-level fall by storing of oceanic waters 

 in continental ice sheets. Obviously, the subtraction of water from 

 the seas to make the ice sheets must have been a slow and on the 

 whole gradual process ; and the time consumed in the growth of the 

 ice sheets probably was not materially shorter or longer than that 

 required in their melting. 



From these considerations it is clearly evident how exceedingly diffi- 

 cult is the proper determination of the part actually played by glacia- 

 tion and ensuing deglaciation in the emergence and submergence of the 

 continental borders. The fall and rise of sea level directly resulting 

 from the storing of oceanic water to make a great ice sheet that later 

 is returned to the sea is so intricately connected and interwoven 

 with genetically similar but at times oppositely directed general and 

 local deformations of land areas and also of sea-bottom areas adja- 

 cent to the strand line, that the reliable valuation of the two or more 

 factors seems as yet practically hopeless. Moreover, it appears to 

 me that only the early and the late stages of a period of glacial con- 

 trol could have made and left anything approaching world-wide 

 and vertically equal records of consequent displacements of the 

 strand line. The early stages would be those in which the lateral 

 growth of the ice sheet had not yet reached the zone in which the 

 weight of the ice would have caused extramarginal bulging and 

 apparent lowering of sea level far in excess of the fall actually 

 occasioned by transferal of water from the sea to the land. Simi- 

 larly the later stages would be those following the retreat of the ice 

 sheet to the same relatively innocuous limits. 



It follows then that only the eustatic smaller shiftings of the 

 Pleistocene sea levels may be definitely ascribed to storing and sub- 

 sequent release of frozen water on the land. And for these even 

 it is mainly their occurrence in a known ice age that induces one to 

 admit their probable glacial origin. However, the larger and in most 

 instances also much more local Pleistocene oscillations of the strand 

 line, even granting that their causation is intimately connected with 

 ice loading and unloading of land areas, belong to another category. 

 Strictly speaking, these larger displacements have resulted from 

 truly diastrophic causes and processes that are concerned with the 

 maintenance of the isostatic equilibrium of the lithosphere. 



Under the circumstances, then, I must agree with Barrell in con- 

 cluding that the amount of water taken from the seas for the forma- 

 tion of the ice sheets was not a direct " major factor in the control 

 of Pleistocene sea levels." Movements, acting within, beneath, and 



