PHYSICAL FEA TUXES OF THE UNITED STA TES 313 



ture must depend on irrigation, just as in the Cordilleras. Here, 

 again, grazing may flourish without need to compete with agri- 

 culture for possession of the land, arid the domain of the herds- 

 man is thus naturally set apart.' 



Of the rarer mineral resources the Central Plain has greatest 

 wealth in coal, which underlies broad tracts and is easily mined. 

 It is rich also in iron, both Plutonic and Apollonic, and has 

 abundant salt and gypsum. Throughout its broad extent wagon 

 roads and railroads are easily constructed, and its grain for ex- 

 port finds cheap water transportation from interior districts to 

 the sea by way of the Mississippi and the St Lawrence. 



The mountains of the Appalachian Province were formed by 

 the cooperation of Pluto and Apollo. Long ago the crustal rocks 

 were crowded together in a great system of wrinkles, the crests 

 of which were then wholly pared away so that the Central and 

 Atlantic plains were joined in one. Then came other disturb- 

 ances along the folded belt, but without new folding. The plain 

 was locally lifted into a long plateau, with gentle slopes on either 

 side, and from this plateau the mountains have been carved. 

 Through the remnants of the old truncated folds ran long out- 

 crops of various and diverse rocks, trending northeast and south- 

 west, and these rocks have been wasted unequally by the eroding 

 waters. Where there were soluble limestones or weak shales, the 

 streams opened valleys; where there were resistant sandstones 

 or quartzites, mountain ridges were left ; and so the Appalachian 

 ranges are a complex cameo of Nature's carving. The broader 

 valleys were smoothed in the carving and prepared for agricul- 

 ture, the mountains left rough and reserved for forest. The region 

 is rich in iron, both Apollonic and Plutonic, and peculiarly rich 

 in what may be called Plutonic coal — coal made, indeed, by 

 Apollonic processes, but converted to rich anthracite by Plutonic 

 heat. Water power is abundant, and though less magnificent in 

 its possibilities than the power associated with the loftier Cor- 

 dilleras, of greater present value because more tractable, and 

 because associated with tillable plains that are qualified by cli- 

 mate for the primary industry of agriculture. 



The Atlantic plain resembles the Central in that both cutting 

 and filling have contributed to its formation, but the constructive 

 factor is here more important. While the Appalachian folds were 

 being reduced, part of the waste went eastward, burying the At- 

 lantic margin of the continent and extending it seaward. Later, 

 when the Appalachian cameo was carved, the accumulation of 



