166 A. Guyot on the Appalachian Mountain System. 
is formed, in the east, by a plain slightly inclined towards the 
‘Atla ntic. The width of that plain, in New inaiont does not 
sede much from fifty miles. Near the mouth of the Hudson, . 
however, in New Jersey, it nearly disappears, but gradually i ine 4 
state towards the south to a width of over two hundred mi 
Its elevation above the sea, at the foot of the mountains, ‘aul a 4 
New Boglond, from 800 to 500 feet. From the neighborhood 
of the of New York, where it is nearly on a level with the 
ocean, it. rises gradually 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 altitude of the 
Ohio een full one-half from that of the surrounding lan 
elt of the Appalachian highlands forms the mar- 
gianis ast of the American continent on the Atlantic side, and. 
termin 4 
ae uniform, Toms not, like the Alps, or the other great 
tems of fracture, have a central or main axis, to which the 
secondary cnet ate 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 gen- 
eral height of the chains is sensibly equal and their summits 
show sii many nor deep mealies, In the middle region, es 
pecially in Pennsylvania and New Jersey, they present t the oe 
pearance of long and continuous sala the blue summits of whi 
trace Sng the horizon a uniform line seldom varied by any — 
peas’ or crags. In the extreme northern and southern portions, 
owever, this character opr aks modified: There the sys 
om. : : d : 
= 
There is one feature of the A palachian system which distin 
guishes it from the ranges of the ' nae it is the well marked divis- 
jon into two longitudinal zones £ elevation, one turned towards 
the shores of the Atlantic, in ky the form of parallel chains 
just spoken of predominates, ae the other turned towards 
interior, which is composed of elevated and continuous plateaus, 
descending from the summit of their eastern escarpment, in the 
centre of the system, in gentle stages towards the basins of | 
lakes and the valley of the Ohio. Occasionally minor chains, ver} 
little elevated from their base, wrinkle the per of the ta 
lands. Their parallelism with those of the eastern 
