GULLIVER. — SHORELINE TOPOGRAPHY. 177 



controlling wave-base. The term wave-base is here introduced as a com- 

 parable term to river baselevel or hard stratum baselevel. It is another 

 local baselevel, which ought to be distinguished from the grand baselevel 

 of the sea. 



Thus, at a late stage of development, the peneplain and the submarine 

 platform almost merge into each other; indeed, so murh do the forms 

 resemble each other, that the one process or the other has been given by 

 many writers as explaining the total degradation toward a plain. The 

 plain of marine denudation, perhaps better called the submarine platform, 

 is distinguished from the peneplain by its cover of offshore deposits, and 

 the limits of this cover, even after it is partly stripped off, can be found 

 from the arrangement of the drainage. 



The need for a separate term for the controlling plane from that of the 

 surface, down to which the forces of degradation are able to reduce the 

 land, is shown when o'ne examines recent writings upon this subject. To 

 speak of the deformation of the baselevel* is like saying a bent cone in 

 conic sections. Both terms imply abstract mathematical surfaces that 

 cannot suffer distortion. The peneplain may be uplifted, tilted, warped, 

 or folded, but not the baselevel. In the same way it is helpful to distin- 

 guish between the submarine platform and the wave-base. The offshore 

 erosion surface will approach the depth to which the maximum wave 

 action is possible, but the submarine platform will be cut to that depth 

 only in the zone of maximum wave activity. 



Sea Transportation. — When the sujiply of waste has increased beyond 

 the power of the various currents to immediately deposit it offshore, 

 transportation alongshore will become more important, and aggradation 

 may take place in certain places. The tendency of shore currents is 

 undoubtedly to form curves in the shoreline wliich will be satisfactory 

 to the particular current acting. 



The writer makes the following distinction between the sea action 

 upon the inner shoreline, which includes the more protected coasts of 

 bays, drowned valleys, sounds, channels, etc., and its action upon the 

 outer t shoreline, which is that of the exposed coasts of the ocean. The 

 ocean currents have little direct effect upon the inner shoreline, and the 

 wind has not opportunity to develop, by the formation of waves, current 

 eddies of large radius of curvature upon inland waters. In these narrow 

 arms of the sea the tidal currents are the preponderating force, for here 



* Diller, 14th Ann. Rep. U. S. G. S., 1892-93, Part II., 406; Jour, of Geol., 1894, 

 IL 45. 



t See Penck, loc. cit., II. 551. 

 VOL. XXXIV. — 12 



