in the Pleistocene and Post- Pleistocene. 5 



eroded, that marine denudation for the whole earth at present 

 amounts to probably between - 02 and "10 cubic miles per year, 

 whereas the rivers bring to the sea annually probably between 

 1*50 and 3 - 00 cubic miles of rock material. These wide limits 

 must be used, since for the earth as a whole the data are as yet 

 not on a quantitative basis. But to have any application to 

 the geologic past the variation in rates of erosion of both 

 marine and subaerial agencies, and the high or low values of 

 the present rates, must be considered. Now an examination of 

 present shores shows that they are characteristically young and 

 the sea work is mostly erosion at certain parts of the shore, not 

 upon the bottom. Beyond some miles off shore, deposition is 

 in general taking place. In the oscillations of sea level the last 

 movement therefore has, on the whole, been one of sub- 

 mergence and this phase is favorable for a large proportion of 

 gravel in the marine deposits now in evidence near the shores. 



Turning to the application to the present subject, it appears, 

 by reversing the argument, that recent movements of the strand 

 line may be elucidated by a method of study which analyzes 

 the place and character of marine degradation and aggradation ; 

 a study pursued in a somewhat similar fashion to that study of 

 fluviatile degradation and aggradation which has thrown such 

 great light on the succession of crustal movements. Both 

 rivers and sea work with i-espect to a base level. Their first 

 effort is to bring a profile to a graded slope, eroding in 

 some places, depositing in others. For the one as for the 

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

 relative duration of recent changes of level. Valuable studies 

 on the principles controlling the character of the shore line 

 have been made by Davis and Gulliver, but what is here 

 emphasized is the study of the water bottom, both near shore 

 and offshore, its sedimentary character and its form. The basis 

 for study consists especially of the hydrographic charts issued 

 for the use of mariners. The writer has used particularly 

 those published by Great Britain and the United States. The 

 form of the bottom may be advantageously studied, not only 

 from the plan, but by means of the projected profile. For this 

 a section plane is taken at right angles to the submarine con- 

 tours, and, to smooth out the minor effects of currents and 

 waves and to make up for the scantiness and possible errors of 

 the data, all soundings within a certain width are projected 

 upon it and located as dots. A smoothed curve is then drawn 

 through the soundings. These profiles are illustrated in 

 figures 1 and 2. 



In such studies distinction must be drawn between the sub- 

 aqueous profiles of aggradation and degradation. Although in 

 the course of unlimited time the two would tend to approach 



