MOUNTAIN RANGES. 209 
' tern is composed of rocks of the transition class, or 
the oldest formations of the non-fossiliferous sec- 
ondary group. The Appalachian belt consists of 
secondary rocks of the oldest kind, containing fossils, 
but no rocks as recent, apparently, as the bitumi- 
nous coal series. The Alleghany range is composed 
also of secondary formations, which seem to owe 
their configuration, which is that of vast piles of 
nearly horizontal strata, rising from a plain inter- 
sected by innumerable deep valleys of denudation, 
to causes which seem to have removed part of the 
high plateau on which they stand, rather than to di- 
rect uplifting forces, such as appear to have eleva- 
ted the more irregular and convulsed systems of the 
other three mountain systems. 
Thus nearly the w^hole of North America is di- 
vided into two immense plains, the one lying be- 
tween the Atlantic and the Appalachian or Allegha- 
ny Mountains, and extending from Long Island to 
the Gulf of Mexico ; the other, which may be called 
the central basin of the continent, from the Alle- 
ghanies to the Rocky Mountains, and expanding 
from the Gulf of Mexico, widening as it stretches 
northward until it reaches the Arctic Sea and Hud- 
son's Bay. The first great plain, extending from 
the Atlantic to the adjacent mountains, is, in the 
Southern states, nearly 200 miles in breadth, and 
throughout its whole extent it is separated into two 
tracts, strongly contrasted with each other both as 
respects their geographical and geological features. 
The boundary which divides them is the eastern 
edge of a low, undulating line of primary rocks, 
which, forming the termination of the upper or 
rocky tract, separates it from the lower flat and 
sandy plains, with every appearance of having been 
at one time the line of the coast. 
From New- Jersey to North Carolina, this bound- 
ary, beginning the rocky country, presents a well- 
marked barrier to the tide in nearly all the rivers 
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