498 H. E. Gregory — Formation and Distribution of 



becomes a shoal without the intervention of significant old-age 

 forms other than the " flying bars." 



The profile of the shore also advances to maturity as the 

 result of normal shore erosion, transportation and deposition 

 within a single cycle. Shore maturity is usually reached after 

 coastal maturity has been attained, and in fact is made possible 

 in large part by the establishment of coastal maturity, for the 

 simplification of the coast line by cutting off headlands and 

 building bay bars is to be considered not as a phase of the con- 

 test between sea and land as is frequently stated, but rather as 

 a stage in the process of development of shore equilibrium. 

 Like the coast contour, the shore profile does not advance past 

 maturity on continental borders where land remains uncon- 

 sumed ; but on shoals representing former islands, old age 

 may be attained and the surface of the underwater land may 

 continuously progress toward wave base. The normal shore 

 profile both on cutting and building coasts " is a compound 

 curve which is concave near the shore, passing through aline of 

 little or no curvature to a convex front." * The attainment of 

 this profile of equilibrium is accomplished only after the ex- 

 penditure of an enormous amount of energy on a complicated 

 piece of work, but the advantages are correspondingly great, 

 for in consequence of previous establishment of coast maturity 

 the coast is now openly exposed to the attack of the waves for 

 long stretches of straightened shore line and wave energy may 

 now be concentrated within the zone where it is roost effective. 

 The position of the profile changes with the migration of the 

 shore line ; with constant sea level it moves landward. The 

 form of the profile appears to remain constant, but its relative 

 dimensions change in response to the type of initial coastal 

 belt, wave power, and mass of materials provided for trans- 

 portation. 



Steepness and regularity of slope are factors which affect 

 the distances to which materials may be carried, for waves tend 

 to establish conditions where their greatest abrasive energy is 

 concentrated along a narrow belt, the breaker line, and where 

 the profile is of such steepness as to allow for ready seaward 

 transportation of materials provided. An initially over-steep 

 slope retards wave action in carrying material seaward, for the 

 materials worn from cliffs are deposited near the shore line 

 until the profile is placed in adjustment. An initially over-flat 

 profile likewise retards coast erosion, for under such conditions 

 the locus of wave attack is some distance off shore, and before 

 the waves may reach the coast a notch must be cut on the bottom, 

 and a bar, or a series of bars, as the waves again and again re- 

 recover their form, be thrown up. The net result is that much 



*Fenneman, Jour. Geol., x, p. 27, 1902. 



