CHAPTER XIX 



COAST RECORDS OF THE RISE OR FALL OF THE 



LAND 



The characters in which the record has been preserved. 



The peculiar forms into which the sea has etched and molded its 

 shores have been considered in the last chapter. Of these the 

 more significant are the notched rock cliff, the cut rock terrace, 

 the sea cave, the sea arch, the stack, and the sloping cliff and ter- 

 race, among the carved features ; and the barrier beach and built 

 terrace, among the molded forms. It is important to remember 

 that the molded forms, by the very manner of their formation, 

 stand in a definite relationship to the carved features; so that 

 when either one has been in part effaced and made difficult of de- 

 termination, the discovery of the other in its correct natural posi- 

 tion may remove all doubt as to the origin of the relic. 



In studies of the change of level of the land, it is customary to 

 refer all variations to the sea level as a zero plane of reference. 

 It is not on this account necessary to assume that the changes 

 measured from this arbitrary datum plane are the absolute up- 

 ward or downward oscillations which would be measured from the 

 earth's center ; for the sea, like the land, has been subject to its 

 changes of level. There need, however, be no apology for the 

 use of the sea surface as a plane of reference ; for it is all that we 

 have available for the purpose, and the changes in level, even if 

 relative only, are of the greatest significance. It is probable that 

 in most cases where the coast line is rising from uplift, some por- 

 tion of the sea basin not far distant is becoming deepened, so that 

 the visible change of level is the algebraic sum of the two effects. 



Even coast line the mark of uplift. It was early pointed out 

 in this volume (p. 158) that the floor of the sea in the neighborhood 

 of the land presents a relatively even surface. The carving by 

 waves, combined with the process of deposition of sediments, tends 

 to fill up the minor irregularities of surface and preserve only the 



245 



