2IO 



University of California. 



[Vol. 2. 



On a rising coast, where the subaerial and submarine slopes are 

 at a high angle, and the cliffs correspondingly high, the compara- 

 tively narrow terraces formed are more rapidly obliterated through 

 marine abrasion, after uplift, than in the case of a low angle of 

 subaerial and submarine slope, and correspondingly low cliffs, with 

 the resulting broader platforms, provided other factors are the 

 same in both instances. This may be illustrated by the following 

 example. Given two cliffs such that the ratio of the volumes of 

 the material cut in the two cases, for every horizontal foot cut 

 back, along a given length of coast line, is as one to five. This 

 ratio will be given by slopes with a rise of ten feet and fifty feet, 

 respectively, in every hundred feet — corresponding to angles of 

 5° \2' 38" and 26 33' 54" (angles A' C D' and ACD in figure 3). 



Figure 3. 



To simplify the conditions of the problem, the cutting may be 

 assumed to be in homogeneous rocks, and all other factors except 

 slope (such as character of rocks, fetch of the waves, strength and 

 character of the off-shore currents, etc.) may be considered as the 

 same in the two cases. Further, we may neglect the fact that the 

 sea cliffs are not perpendicular, and also the amount of coastal 

 detritus deposited on the submarine slopes beyond the platform 

 cut by the waves, since neither of these factors (uncertain in any 

 case) would materially affect the general result. 



Since, at the outset, with the sea-level C'B' — CB, the submarine 

 slope CD is the steeper, the waves will be longer in making an 

 active start in cliff cutting than on the slope A'C'D'. Although 

 this difference is an important one, it may be set aside for the 

 present, as it will be taken into account later. Considering, then, 

 that in a prolonged period of wave cutting, equal volumes are 

 removed in a given time in the two cases, it follows that when a 

 distance CB' of 1,500 feet has been cut in the gentler slope, a 



