2l6 



University of California. 



[Vol. 2 



distribution and deposition of the eroded material, and therefore the 

 less the deposition immediately offshore or along shore. It may be 

 noted here that, in general, the greater the amount of drift passing 

 any given point along a coast line and derived from other parts of 

 the coast, the less rapid will be the cutting at that point; since the 

 drift thus transported must be disposed of by waves and currents, 

 in addition to that derived from the immediately adjacent shore 

 line. 



A terrace formed during a slow depression will be broader, 

 other things being equal, than one formed during a slow elevation. 

 For, during depression the off-shore depths are slowly increased as 

 the cliffs recede under the attack of the waves, thus avoiding, to a 

 greater or less extent, the continuous submarine erosion otherwise 

 necessary to continuous cliff cutting. On the other hand, elevation 

 only increases the difficulty to be overcome, necessitating more than 

 the normal erosion to keep the off-shore depths sufficiently great 

 for active cliff cutting. It is possible that the width of the present 

 submarine terrace is due in part to a very slow depression of the 

 coast during the earlier stages of its development. 



From the comparative study made of wave-cut shore features, 

 it appears that, of all the foregoing single factors concerned in the 

 production of pronounced terracing, that of cliff height, normally 

 dependent on slope, is the most important, provided the waves have 

 the minimum fetch necessary for active cutting. 



Preservation of Elevated Wave-Cut Terraces. — We have next to 

 consider under what conditions terraces, after elevation, best resist 

 the subaerial forces of destruction. If terraces are equally well 

 developed in hard and soft rocks, on surfaces of moderate slope 

 and not greatly dissected, they would be better preserved in the 

 hard rock. For, in order to have equal development in the two 

 cases, it would be necessary, in general, that the slope in the 

 harder rocks should be at least as low as that in the softer; and, 

 with equal slopes, general subaerial erosion (and consequently ter- 

 race obliteration) is more rapid in the soft than in the hard rocks. 

 With equally abrupt cliffs at the rear of the terraces, those in the 

 harder rocks would preserve their sharp outlines for a longer time, 

 those in the soft rocks soon becoming softened and rounded in 



