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PHYSICAL GEOLOGY 



alternating bands of lowland and highland, the lowland being bordered on the sea- 

 ward side by infacing cliffs formed by the harder beds. The low ridges thus developed 

 have a steep descent on one side and a gentle slope on the other and are called cuestas. 

 Examples of coastal plains with this banded arrangement are not uncommon. In 

 Alabama the Appalachian Mountains are bordered by the " Black Prairie," a belt 

 of lowland formed in easily eroded limestone. Next to this is a ridge (cuesta) which 

 ascends rather abruptly 200' feet above the lowland, composed of more resistant lime- 

 stone (Fig. 217 A, B). The geological structure of the Ghats in India (Fig. 207 

 p. 216) shows the formation and characteristics of such topography. Very ancient 

 coastal plains with resulting cuestas constitute a large part of New York, Ohio, and 

 other states. 



Rough Shores. — By marine erosion a shore may be slightly rough- 

 ened, but it is not possible for waves unaided to make irregular shores 



like those of the coast of 

 Maine, Nova Scotia, Wash- 

 ington, northern Europe, 

 British Columbia, and the 

 coast of the Adriatic. Such 

 shores are formed by the 

 sinking of the land or the 

 raising of the sea level. When 

 a region is partially sub- 

 merged the higher hills be- 

 come islands or peninsulas, 

 and the valleys become estu- 

 aries or bays. Consequently, 

 rugged coasts bordered by 

 high, rocky islands (Fig. 218), 

 are evidences of subsidence. 

 An interesting example is to be 

 found in northeastern North 

 America, where the coast line 

 between New Brunswick and 

 Portland, Maine, is 2000 miles 

 long, although a straight line 

 between the points is only 

 200 miles in length. 

 Another characteristic of a sunken coast is the existence of sub- 

 marine valleys. On the coasts of Europe and North America sound- 

 ings have shown that the valleys of rivers extend far out on ancient 

 coastal plains (Fig. 219), now the sea bottom. The Hudson River 



Fig. 218. — Portions of the coast of Maine, 

 showing the effect of subsidence. The valleys 

 have become bays, and the hills peninsulas and 



islands. 



