414 barrell: movements of the strand line 



Since the Oligocene the strand line has, on the whole, been 

 retreating, the continents rising higher, the climates growing 

 colder. In the Pleistocene there seems to have been a culmi- 

 nation of crustal and climatic oscillations, followed by a descend- 

 ing series. From these facts the ice age has been looked upon 

 as past and the Quaternary revolution as closing, but at several 

 times within the Pleistocene that view would have been better 

 justified on the basis of a descendin^series than it is at the present 

 moment. 



Indications of oscillations given by subaqueous profiles. From 

 a study of present shore action made some years previously as 

 a basis for the development of "Some distinctions between 

 marine and terrestrial conglomerates,"- it appeared that recent 

 movements of the strand line may be elucidated by a method 

 of study which analyzes the place and character of marine ero- 

 sion and sedimentation. Both rivers and sea work with respect 

 to a base level. Their first effort is to bring a profile to a graded 

 slope and the nature of the work shows the direction, amount, 

 and relative duration of recent changes of level. In order to 

 study the water bottom the writer has made use of hydrographic 

 charts of soundings. Profiles at right angles to the submarine 

 contours have been obtained by projecting upon the given sec- 

 tion all soundings within a certain width. A smoothed curve 

 is then drawn through the soundings. Thus minor irregulari- 

 ties and possible errors tend to be eliminated. Such profiles 

 show for many coasts that the present profile of wave-action is 

 about 20 fathoms above a previous stand, this conclusion being 

 in accord with the results reached by both Daly and Vaughan. 

 Professor Daly has been following independently the same line 

 of investigation and he states in a personal communication 

 that he has reached the conclusion that effective wave-action 

 stops much above the conventionally accepted 100-fathom line. 

 With this conclusion the writer is in accord, and as an impli- 

 cation it appears that the outer flats of continental shelves are 

 wave-built terraces constructed mostly from river detritus and 

 laid down during lower stands of the sea. Drowned river val- 



2 Abstract, Bull. Geol. Society of America, 20: 620. 1908. 



