Physical geography. By Mary Somerville ...

CHAP. XII. THE ALLEGHANIES. 129
Although the subsoil is perpetually frozen at the depth of a few
feet below the surface beyond the 56th degree of north latitude, yet
trees grow in some places up to the 64th parallel. Farther north
the gloomy and majestic forests cease, and are succeeded by a bleak,
barren waste, which becomes progressively more dreary as it approaches the Arctic Ocean. Four-fifths of it are like the wilds of
Siberia in surface and climate, covered many months in the year
with deep snow. During the summer it is the resort of herds of
rein-deer and bisons, which come from the south to browse on the
tender short grass which then springs up along the streams and
lakes.
The Alleghany or Appalachian chain, which constitutes the second
or subordinate system of North American mountains, separates the
great central plain from that which lies along the Atlantic Ocean.
Its base is a strip of table-land, from 1000 to 3000 feet high, lying
between the sources of the rivers Alabama and Yazoo, in the southern states of the Union, and New Brunswick, at the mouth of the
river St. Lawrence. This high land is traversed throughout 1000
miles, between Alabama and Vermont, by from three to five parallel
ridges of low mountains, rarely more than 3000 or 4000 feet high,
and separated by fertile longitudinal valleys, which occupy more than
two-thirds of its breadth of 100 miles. In Virginia and Pennsylvania, the only part of the chain to which the name of the Alleghany mountains properly belongs, it is 150 miles broad, and the
whole is computed to have an area of 20,000 square miles. The
parallelism of the ridges, and the uniform level of their summits,
are the characteristics of this chain, which is lower and less wild
than the Rocky Mountains. The uniformity of outline in the southern and middle. parts of the chain is very remarkable, and results
from their peculiar structure.' These mountains have no central
axis, but consist of a series of convex and concave flexures, forming
alternate hills and longitudinal valleys, running nearly parallel
throughout their length, and cut transversely by the rivers that flow
to the Atlantic on one hand, and to the Mississippi on the other.
The watershed nearly follows the windings of the coast from the
point of Florida to the north-western extremity of the State of
Maine.
The picturesque and peaceful scenery of the Appalachian mountains is well known; they are generally clothed with a luxuriant
vegetation, and their western slope is considered one of the finest
countries in the United States. To the south they maintain a distance of 200 miles from the Atlantic, but approach close to the coast
in the south-eastern part of the State of New York, from whence
their general course is northerly to the river St. Lawrence. But
1 Sir Charles Lyell's Travels in North America,