314 PROCEEDINGS OP THE AMERICAN ACADEMY. 



Typical Shore Profiles. 

 A graded profile being ouce attained, its graded condition will be 

 preserved through all the rest of an undisturbed or normal cycle of 

 shore development ; shore profiles and river profiles being alike in this 

 as in so many other respects. Before grade is assumed, the ability of 

 the sea may be so far in excess of its load that it undercuts the shore 

 and forms sea caves at tide level, as in profile 1, Figure 2. When 

 grade is first assumed, the coast is usually cut back to a steep cliff, like 

 profile 2. Much later, when the sea has cut back the shore so that 

 the waves must transverse a submarine platform before attacking the 

 laud, their strength is thereby so much lessened that the cliflf leans 

 back to a moderate slope, as in profiles 3 and 4, and even then supplies 

 enough waste to keep the waves at its foot fully occupied. 



Fig. 2. 



There is something more than analogy in the comparison that may 

 be drawn between the longitudinal profile of a stream and the trans- 

 verse profile of a shore. In youth, each usually has its torrent or 

 upper portion, where ability to carry load is greater than load to be 

 carried ; but as development progresses, the graded couditiou of mid- 

 stream extends headward, and after a time reaches all the way to the 

 headwaters. At the same time, the lower or fioodplain-delta portion 

 extends seaward, its grade being rather steeper in adolescence, when 

 nmch material is brought from the headwaters, than later, in maturity 

 and old age, when the supply of waste is very slow. The critical point, 

 wliere marine action changes from degrading the near-shore bottom to 

 aggrading the ofF-shore bottom, migrates seaward, as 1', 2', 3', 4', in 

 Figure 2. At the same time, the seaward extension of the bottom 

 deposits increases. Furthermore, the comparison between stream and 

 sea suggests the need of examining that process on the sea floor, which 

 corresponds to corrasion in the stream bed. Sea-shore profiles make 

 it clear that a considerable deepening is accomplished on the floor of 

 the platform, landward from the critical points, 1', 2', etc. Off the 

 eastern cliif of Cape Cod, this deepening can hardly have been less 

 than fifteen or twenty fathoms : off the Chalk cliffs of Normandy, a 

 similar scouring and deepening of the bottom may be inferred. We 



