ulrich: major causes of oscillations 65 



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 adjacent 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 control could 

 have made and left anything approaching world-wide and 

 vertically equal records of consequent displacements of the 

 strandline. 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. 

 Similarly 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 subsequent 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 strandline, even granting that their causa- 

 tion 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 concluding that the amount of water taken from the seas for 

 the formation of the ice sheets was not a direct "major factor 

 in the control of Pleistocene sea levels." Movements, acting 

 within, beneath, and upon the lithosphere thus appear to have 

 been the more effective factors. 



That the marginal areas of the continents were at times 

 elevated and folded is, of course, accepted by all — even by 

 Suess and his followers, who speak of the continents as having 

 the character of "horsts" and of the ocean basins as being perma- 



