52 Professor Guyot on the Physical Geography 



which kindly forwarded to us, we extract the following general 

 conclusions as to the physical structure of the chain. 



" The upheavals of ancient rocks which constitute this well connected 

 physical structure, for which, as a whole, it is proper to retain the 

 common name of the Appalachian system, extend in an undulating line 

 thirteen hundred miles in a mean direction of N. E. to S. W., from the 

 promontory of Gasp6 upon the Gulf of St. Lawrence to Alabama, 

 where the terminal chains sink down and are lost in the recent and 

 almost horizontal strata of the cretaceous and tertiary formations which 

 cover the greater portion of the surface of this state. This long range 

 of elevations is composed of a considerable number of chains, sensibly 

 parallel to each other, occupying more particularly the eastern part 

 which faces the ocean, and of an extended plateau which prevails to- 

 wards the west and northwest and descends gradually towards the 

 inland valleys of the St. Lawrence, the lakes Erie and Ontario and the 

 Ohio River. 



The base on which this large belt of mountains rests, and which may 

 be considered as bounded by the Atlantic Ocean on one side and by the 

 Ohio and St. Lawrence Rivers on the other, is formed, in the east, by a 

 plain slightly inclined towards the Atlantic. The width of that plain, 

 in New England, does not vary much from fifty miles. Near the mouth 

 of the Hudson, however, in New Jersey, it nearly disappears, but gra- 

 dually increases towards the south to a width of over two hundred 

 miles. Its elevation above the sea, at the foot of the mountains, is in 

 New England, from 300 to 500 feet. From the neighborhood of the bay 

 of New York, where it is nearly on a level with the ocean, it rises gra- 

 dually towards the south to an altitude of over 1000 feet. On the west 

 the table-lands which border upon the Ohio River, and which may be 

 considered as the general base of the system, preserve a mass-elevation 

 of a thousand feet or more, in the thickness of which the river bed is 

 scooped out to the depth of from 400 to 600 feet, thus reducing the alti- 

 tude of the Ohio River full one-half from that of the surrounding 

 lands. 



The vast belt of the Appalachian highlands forms the marginal bar- 

 rier of the American continent on the Atlantic side, and determines the 

 general direction of the coast line, which in general, runs parrallel to 

 the inflections of its chains with remarkable regularity. This system, 

 composed of a series of corrugations tolerably uniform, does not, like 

 the Alps, or the other great systems of fracture, have a central or main 

 axis, to which the secondary chains are subordinated. But it is properly 

 compared to the system of the Jura, for it is composed like that of a 

 series of long folds, or chains, which run parallel to each other, often 

 with great regularity. In the same part of the system the general 

 height of the chains is sensibly equal and their summits show neither 

 many nor deep notches. In the middle region, especially in Pennsylva- 

 nia and New Jersey, they present the appearance of long and continuous 

 walls, the blue summits of which trace along the horizon a uniform line 



