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University of California. 



[Vol. 2. 



unusually favorable one for the study of certain shore features, 

 particularly terraces. The conclusions drawn from the study of 

 the phenomena in this region have been verified, as far as possible, 

 by comparison with other regions of the United States where 

 similar features are found. Gilbert's classic work* has, of course, 

 furnished most of the fundamental principles involved. 



The principle which it is desired to emphasize throughout this 

 section of the paper is the dependence of the development of shore 

 features on the character of the subaerial coastal topography. 



If a given region long subjected to the forces of subaerial ero- 

 sion is depressed, the off-shore slopes will necessarily be those 

 characteristic of subaerial erosion. Along the immediate coast line 

 the subaerial slopes, before depression, will of course have been 

 modified to a greater or less extent through marine action in the 

 process of forming sea cliffs, so that they may present a consider- 

 ably steeper angle than that due to subaerial erosion alone. In any 

 case, however, the erosion slopes will be gentler in the less resistant 

 rocks, and the off-shore slopes after submergence will therefore be 

 less, than in the case of the more resistant rocks. The more resist- 

 ant the rocks to erosion, the greater will be the angle of slope. 

 The least submarine slope will be given by areas of sedimentation, 

 as the floors of broad valleys carried beneath sea level. 



If, on the other hand, after a long period of comparative quies- 

 cence, a moderate elevation occurs, the immediate on- and off-shore 

 slopes will be those characteristic of the subaqueous platform pro- 

 duced by marine abrasion, and therefore of a very low angle. This 

 is the present condition on the Atlantic Coast, while the former con- 

 dition prevails on the California coast. At the close of the Miocene 

 the California coast was elevated more than at present, in all prob- 

 ability some 3,000 feet. After a prolonged period of erosion it 

 was submerged, and in the rise that followed, the post-Miocene 

 elevation of the land was only in part recovered. It is therefore 

 assumed that the average on- and off-shore slopes of the California 

 coast are in general those characteristic of subaerial erosion, modi- 

 fied near the present sea-level by a prolonged period of wave action 

 which has formed the submarine platform, or " continental shelf," 



*U. S. Geol. Surv. , Monograph I, 1890. Lake Bonneville. 



