218 



University of California. 



(VOL. 2. 



cince, with its accompanying moderate dissection and moderate 

 angle of on- and off-shore slope, is best fitted for the development 

 and preservation of wave-cut features. 



Some of the best developed and preserved terraces along the 

 California coast are in the Miocene shales,* which furnish the 

 conditions just laid down. 



The principles here stated are illustrated along the California 

 coast generally, as well as on the islands which have been espe- 

 cially considered. Terraces are found well developed in the softer, 

 iittle dissected rocks, where moderate slopes are presented to wave 

 action. They are found little or not at all developed in the more 

 rugged forms, with high angle of slope, characteristic of mature 

 topography in hard rocks; and where developed, they are, in 

 general, but imperfectly preserved. The difference in the character 

 of the topography and evidence of terracing is not, therefore, a 

 certain indication that the two forms have not been subjected to 

 the same conditions, as regards both subaerial erosion and terrac- 

 ing. So that the more recent movements of the islands as a 

 whole have not been the same, can not be predicated from the 

 presence or absence of terraces, so long as the topographic forms 

 are such as to warrant, on the principles already laid down, a 

 terraced structure in one case, and a non-terraced, or but slightly 

 terraced, condition in another. There are many miles of rugged, 

 unterraced topography along the mainland coast of California, 

 adjacent to forms yielding pronounced terraces. 



The position of San Clernente Island, as regards terracing, is 

 exceptional for the California coast, primarily because of the com- 

 bination of hard rocks with low angle of slope. This combination, 

 on a generally mature coast, could be due only to accident. 

 Through faulting, a very slightly dissected surface of low angle 

 of slope has been presented to wave action in the direction from 

 which the greatest waves come. As we have thus a combination 

 of the most important factors in both the development and preser- 

 vation of terraces, the natural result is a remarkably well-developed 

 and well-preserved series. 



*See, Lavvson, The G;omorphogeny of the Coast of Northern California, 

 Bull. Dept. Geol., Univ. Calif., Vol. I, No. S, 1S94, p. 247. 



