JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. V 



JUNE 19, 1915 



No. 12 



GEOLOGY. — Factors in movements of the strand line.^ Joseph 

 Barrell, Yale University. 



Within recent years new points of view in regard to present 

 and recent movements of the sea level have been developed by 

 a number of geologists. Johnson, Daly, Vaughan, and Davis 

 have made important contributions. The writer has not en- 

 tered upon this subject as a special problem for research but 

 in the pursuit of other investigations has several times come into 

 contact with it. But coming unexpectedly upon a subject from 

 an angle is apt to give new suggestions and somewhat novel 

 points of view. In the brief treatment which is necessary here, 

 the purpose is to outline controlling factors, putting the emphasis 

 upon those aspects which have presented themselves as some- 

 what novel. It is not the plan to demonstrate fully any single 

 thesis, nOr to treat in proper proportion all the composite factors. 



The interpretation of composite rhythyns. The movements of 

 the strand show a rhythmic character. Smaller undulations 

 are superposed upon larger oscillations. In the interpretation 

 of these rhythms attention has generally been focused upon the 

 marks of previous inroads of the sea, not upon the limits of its 

 retreats, for these are now concealed. The record of a descend- 

 ing series measures only the sequence from the last maximum 

 of a greater rhythm and does not in itself tell the present trend 

 of the oscillations. 



1 Abstract of a paper presented before the Geological Society of Washington, 

 March 24, 1915. To be published in full in the American Journal of Science. 



413 



