208 



University of California. 



[Vol. 2. 



As a general rule, the gentler the slopes, in a given region, the 

 less resistant the rocks, the gentlest slopes being found in incoher- 

 ent, readily eroded material. The exceptions to this are as indi- 

 cated above, on some very young surfaces. Such very gentle 

 slopes are readily cut by the waves, and usually furnish abundant 

 shore drift The least shore drift is furnished by abrupt slopes in 

 resistant rocks, such as form a considerable proportion of the Cali- 

 fornia coast. 



As regards the age of coastal topography, we may have young, 

 mature, or old coast lines characteristic of any given age of the 

 subaerial topography; and the coastal forms of a given age will 

 differ with the age and character of the subaerial forms on which 

 they are imposed. For example, a young coast line in a region of 

 generally young topography will differ in character from an equally 

 young coast line in a generally mature region. Also, since the 

 characteristics of inland topography of any given age differ accord- 

 ing to the resistance to erosion of the rocks in which they are cut, 

 the original amount of elevation of the surface, etc., the coastal 

 forms of a given age will vary to correspond with such differences. 



Development of Wave-Cut Terraces. — The laws governing the 

 development of a series of terraces on a rising coast must be 

 deduced from a study of the single terrace and the single shore 

 line. Cliff erosion, with the consequent development of a sub- 

 aqueous platform, the principal shore feature with which we have 

 here to deal, is dependent on the action of the waves, concerned 

 principally in erosion, and on the character of the coastal currents, 

 concerned mainly in the transportation of the eroded material. 



The strength of wave action in cliff erosion is dependent on the 

 direction of the prevailing winds, the distance from which the 

 waves come, the direction in which they approach the shore, and 

 on the character and slope of the bottom, as well as on the amount 

 and character of the detritus along the immediate shore line. The 

 stronger the waves the more active will be the erosion; and the 

 swifter the shore currents the more rapid the transportation of the 

 debris, too much of which acts only as a clog to further cliff 

 cutting. 



Wave action is greatest, other things being equal, where there 



