2 JBarreU — Movements of the Strand Line 



But after the complexities of the record have heen correctly 

 deciphered there come the questions of interpretation. The 

 making and unmaking of the great ice sheets must, by deduc- 

 tion, have been the cause of very appreciable fluctuations in 

 the volume of ocean water. To what extent does the record 

 of movement coincide with this cause, or to what extent does 

 the evidence show inductively that there are other equally 

 important or more important causes? The weight of the ice 

 sheets depressed the crust beneath them, but what was its 

 effect on the zone of crust immediately beyond? Among 

 other questions, if it is found that the Pleistocene and post- 

 Pleistocene movements are to a considerable degree unrelated 

 to glaciation, to what degree are they due on the one hand to 

 isostatic movements, including possibly intermittent changes 

 in the volume of ocean basins, movements merely toward 

 crustal equilibrium ; to what degree are they due to deep- 

 seated radial shrinkage of the earth, generating rhythms of 

 tangential compression in the crust ? These factors, together 

 with the effects of changes in crustal density, the effects of 

 erosion, of sedimentation, and possible changes in the volume 

 of ocean water have operated through all past time, but their 

 effects can be most minutely studied and correctly evaluated 

 for the recent geologic past. 



When, in the future, comprehensive answers can be given 

 to these questions, much will have been learned in regard to 

 the nature of crustal movements, and, as the present is the key 

 to the past, better detailed interpretations will be possible for 

 the stratigraphic record of previous geologic periods. 



Within recent years new points of view have been devel- 

 oped by a number of geologists in regard to present and recent 

 movements of the sea level. Among them, D. W. Johnson 

 has shown the necessity for a re-examination of the supposed 

 evidences of present continuing submergence of the Atlantic 

 shore. Daly has suggested that the rise of sea level with 

 deglaciation may account for the appearance of subsidence of 

 coral islands, without requiring any real movement of the 

 crust. Yaughan has come to the view that the development 

 of recent off-shore reef corals is closely related to a recent rise 

 of sea level and that, in general, reef corals flourish broadly 

 only during and immediately following submergent phases of 

 movement. W. M. Davis has developed especially, through a 

 critical re-examination, the evidence given by the topography 

 of the Pacific Islands. 



The writer has not entered 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 unex- 

 pectedly upon a subject from an angle is apt to give new sug- 



