200 H. L. FAIRCHILD POST-GLACIAL UPLIFT OF X. E. AMERICA 



On exposed coasts the tidal variation of the water level inhibited rapid 

 production of shore features, while inland and along the entangled valleys 

 wave action was too weak. Every experienced observer knows that over 

 wide areas where it is certain that standing water existed for ages the 

 surfaces today may show no clear evidence. 



Apart from deltas the constructive shore feature is gravel bars. But 

 their production requires a concentration of coarse material, with favor- 

 able conformation of the shore, and these conditions are rarely fulfilled 

 apart from deltas or kames. A supply of well rounded cobble or coarse 

 gravel is requisite to enable the waters, short-lived at any horizon, to pile 

 the stuff into bars. They need not be sought on shores exposed to erosive 

 action, and scarcely ever on sandy tracts, for reasons previously given 

 (8i, pages 299-301). 



For erosion features perhaps no coast presented more favorable ex- 

 posure than that of Maine. The comparative failure of wave-work there 

 is shown by the following quotations from Stone : 



**At the higher elevation (on the islands of the coast) the surf had time to 

 erode the till from the more exposed shores, but it had not time to form a 

 cliff of erosion in the solid rock before a change of level transferred the wave 

 action to higher or lower rock. In other words, the changes of level of the 

 sea were relatively rapid"' (page 44). 



". . . The fact that those valleys of most uniform slope and exposure to 

 the sea do not show well defined beach terraces proves that at least the fall 

 of the sea proceeded at a nearly uniform rate, unless the pauses at 225 to 230 

 feet and 20 feet be exceptions*' (page 53). 



"The fact that the till was only partially eroded from the outer islands 

 proves that the retreat of the sea was geologically rapid" (page 486). 



To limit the height of an upraised shore to the conspicuous beach fea- 

 tures seen along a slope or valley side, or even to the outer deltas, will 

 nearly always result in serious error. 



VARIATIOX OF BEACH ALTITUDE 



Shore phenomena may be quite unequal in height, even when made in 

 identical water level, on account of variation in the factors or combina- 

 tion of factors concerned in their production. These variables may be 

 noted as (1) tidal range; (2) different exposure to winds and storms; 

 (3) slope, conformation, and character of the shore; (4) topography of 

 the neighboring coast; (5) cliaracter and volume of the detritus; the 

 latter related especially to (6) stream contributions or deltas. 



The variation that an observer might find within a mile might be 10 

 or 15 feet, particularly in comparing bars and cliffs. Even along a con- 

 tinuous bar a difference in the crest height may be 5 feet in a short dis- 

 tance. 



