232 



PHYSICAL GEOLOGY 



terrace, 



After prolonged erosion the marine terrace is widened, both by the 

 cutting back of the shore and by the outbuilding of the wave-built 

 and the littoral currents have a broad road over which 



to move the shore 

 waste. As a result 

 the heads of the 

 smaller bays are 

 filled with sand and 

 pebbles, the larger 

 bays are closed by 

 bars back of which 

 delta deposits are 

 built out, and the 

 rocky islets and 

 stacks are cut away. 

 When the coast is 

 straighter and the 

 marine terrace is so 

 wide that the waves 

 have lost their abil- 

 ity to continue effec- 

 tively their work of 

 cutting back the 

 land, the shores may 

 be said to be in old 

 age. 



The intermediate 

 stage, maturity (Fig. 

 226 C), is reached 

 when the effective 

 work of the waves 

 is at its height; that 

 is, when the sea is 

 attacking the land 

 along a continuous 

 and nearly straight 

 line of cliffs such as 

 one finds on the 

 northwest coast of 

 France to-day. Such 



FlG. 226. — Three block diagrams showing the effect 

 of marine erosion. Diagram A is the shore which would 

 i' Bull if ;i portion of western New England were lowered 

 1000 feet. Diagrams B and C are later stages of the same 

 region, showing the supposed effect of marine erosion on 

 such :i coast. Since the shore shown in C is relatively 

 Stable it is said to he mature. 



