in the Pleistocene and Post-Pleistocene. 3 



gestions and somewhat novel points of view. It is from this 

 standpoint that the following consideration of the subject may 

 be of value. These points of view must be followed further 

 and tested, however, before their results can be correctly and 

 finally evaluated. In that brief treatment which is necessary 

 in order to compress a large subject into the space of a short 

 article detailed demonstrations must be avoided. The article 

 is planned to be suggestive rather than conclusive. The pur- 

 pose is to outline the controlling factors, putting the emphasis 

 upon those aspects which have presented themselves to the 

 writer as somewhat novel. It is not the plan here to demon- 

 strate fully any single thesis, nor to treat in proper proportion 

 all of the composite factors. 



The Interpretation of Composite Rhythms. 



The movements of the strand show a rhythmic nature. 

 Smaller are superposed as undulations upon the larger oscilla- 

 tions, as, on a smaller and far briefer scale, are superposed the 

 rhythms of waves due to wind upon those produced by tidal 

 forces. In the interpretation of these rhythms, as Gilbert has 

 so clearly shown, attention has been focused upon the marks of 

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

 for these are now concealed.* To extend the analogy used by 

 Gilbert, — if at any time we stand upon the shore and look at 

 the lines upon the sand which mark the arrest and turning of 

 previous waves, we see that the highest is the oldest and the 

 successive marks form a descending series in time and inten- 

 sity. We might generalize from this that the motion of the 

 water was subsiding and the sea would therefore soon be at 

 rest ; but no sooner might this conclusion be announced than 

 greater waves roll in, each obliterating the marks of the lesser 

 waves preceding it, effacing also a part of the previous descend- 

 ing series and beginning the record of a new descending series. 

 If we visited the shore at those rare times when a combination 

 of spring tide and heavy on-shore storm raised the water level 

 highest, we would at the moment of culmination see no series 

 but only the single line of the highest wave. A visit at another 

 time would show highest and faintest, as lines of shells and 

 wrack, the marks made long previous during combined highest 

 tide and storm. Below this would be the record, weeks or 

 months younger, developed during the more moderate spring 

 tides. Below this and still younger would be seen the marks 

 of the waves made during the last high tide. Below this 

 would be the series made by the combination of larger and 

 smaller sets of wind-caused waves, the sequence recorded by 



*G. K. Gilbert, Continental Problems, Bull. Geol. Soo. Am., vol. iv, pp. 

 187-189, 1893. 



