JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. io FEBRUARY 4, 1920 No. 3 



GEOLOGY. — Major causes of land and sea oscillations.^ E. 

 O. UivRiCH, U. S. Geological vSurvey. 



That the position of the strandline — 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 shoreline retreated, leaving such 

 features as elevated seaplains and cliffs on the enlarged land 

 areas; at other times the seas advanced on the land, drowning 

 previous river valleys, cutting new seaplains, and laying marine 

 deposits much farther inland than before. These frequently re- 

 curring positive and negative movements of the strandline varied 

 greatly in amount, but on the whole they were rhythmic in oc- 

 currence and volume. But neither the record of these move- 

 ments nor the rhythm that runs through it is at all simple. Most 

 of the criteria by which we determine that submergence has oc- 

 curred in one case and emergence in another are relatively sim- 

 ple and easily applied. But when it comes to correlating the suc- 

 cessive stages of emergence and submergence in different locali- 

 ties, or when we seek to arrange the movements in proper sequence 

 and to determine their relative duration, the problems become in- 

 volved 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 



' Presidential address delivered before the Geological Society of Washington, 

 Dec. 10, 1919. 



57 



