MAJOR CAUSES OF LAND AND SEA OSCIL- 

 LATIONS. 1 



By E. O. Ulrich, 

 United States Geological Survey. 



That the position of the strand line — hence the relation of land 

 and sea levels — is and has ever been subject to change is a fact now 

 established beyond all possible contradiction. The evidence shows 

 that at times the shore line retreated, leaving such features as ele- 

 vated sea plains and cliffs on the enlarged land areas; at other 

 times the seas advanced on the land, drowning previous river val- 

 leys, cutting new sea plains, and laying marine deposits much far- 

 ther inland than before. These frequently recurring positive and 

 negative movements of the strand line varied greatly in amount, 

 but on the whole they were rhythmic in occurrence and volume. 

 But neither the record of these movements nor the rhythm that runs 

 through it is at all simple. Most of the criteria by which we de- 

 termine that submergence has occurred in one case and emergence 

 in another are relatively simple and easily applied. But when it 

 comes to correlating the successive stages of emergence and sub- 

 mergence in different localities, or when we seek to arrange the 

 movements in proper sequence and to determine their relative dura- 

 tion, the problems become involved and often exceedingly complex. 



The evidence presented, especially in the past few years, by 

 Vaughan, Daly, and Barrell seems to prove that at least the marginal 

 parts of the continents have been subjected repeatedly in recent 

 geologic ages to positive and negative displacements of the strand 

 line; also that the vertical element of these oscillations is not uni- 

 form in amount at different places. Considering only the Pleisto- 

 cene to Recent movements, their differential character at once sug- 

 gests 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 retreats occasioned by periodic 

 deformation and deepening of oceanic basins and ensuing slow sub- 



1 Presidential address delivered before the Geological Society of Washington, Dec. 10, 

 1919. Reprinted by permission from the Journal of the Washington Academy of Sciences, 

 vol. 10, No. 3, Feb. 4, 1920. 



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