REPORT ON THE GEOLOGY OF NORTH AMERICA. J 



thence assume a more decidedly south-western course, penetra- 

 ting deeper into the continent as they traverse Virginia, the two 

 CaroHnas, and Georgia, into Alabama. Throughout this range, 

 especially in the middle and southern portions, they are marked 

 by great uniformity of structure, an obvious feature being the 

 great length and parallelism of the chains, and the uniform level 

 outline of their summits. Their total length is about 1200 

 miles, and the zone they cover about 100 miles broad, two 

 thirds of which is computed to be occupied by the included 

 valleys. They are not lofty, rarely exceeding 3000 feet, and in 

 magnitude and grandeur yield immeasurably to the Rocky or 

 Chippewayan Mountains which traverse the opposite side of the 

 continent. 



This last system of mountains, the Andes of North America, 

 skirts the continent on the side of the Pacific in a broad belt from 

 the Isthmus of Panama almost to the Arctic Sea, its extreme 

 northern limit, as defined by Captain Franklin, being far north 

 on the Mackenzie's River. The chains within this zone are 

 many of them very lofty, their average direction, until they en- 

 ter Mexico, being nearly north and south. Within the United 

 States territory they rise abruptly from the sandy plain before 

 described, in longitude about 32^° west from Washington ; and 

 from that meridian nearly the whole way to the ocean the region 

 is mountainous, with elevated sandy plains, and volcanic tracts 

 resembling those of Mexico. The summits of many of the 

 Chippewayan chains are far above the limit of perpetual snow, 

 the highest points being about 12,000 feet above the sea. 



When we regard the grandeur of the dimensions exhibited in 

 these several divisions of North America, the extreme regularity 

 prevailing over great distances both in the plains and systems 

 of mountains, and the straightness and parallelism of these to 

 its long coasts, we are prepared to look for a proportionately 

 wide range and uniformity in its geological features. To com- 

 prehend the relations of our formations to each other, and the 

 true extent of the portion of our geology at present partially 

 developed, the exhibition of which is in fact the main end and 

 object of this Report, a further description, rather more in detail, 

 of our geography is here requisite. 



Let us first contemplate that long and comparatively narrow 

 plain defined above, which lies between the Atlantic Ocean and 

 the chains of the Alleghany mountains. This tract, which in the 

 New England States is very narrow, comprising the mere coast 

 and islands, expands in its course southward, the mountains in 

 Carohna being more than 200 miles from the sea, It is divided 

 longitudinally nearly through its whole length by a well marked 



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