Appalachian Mountains, the great range of mountains, called also the Alleghanies, which extends from that part of Canada lying between the New England states and the St. Lawrence river, through the whole length of Vermont, across the western part of Massachusetts and the middle Atlantic states, to the northern part of Alabama. The name Appalachian was given to the mountains by the Spaniards under De Soto, who derived it from the neighboring Indians. The name Alleghany, given by the English settlers of the north, was received from the Indians, and supposed to mean endless. The White mountains of New Hampshire and the Adirondack mountains of New York are really outliers of this range, though separated from it by wide tracts of low elevation. In their Alpine forms and more metamorphic structure, they present also features somewhat different from those which are especially peculiar to the Appalachian range. The Cats-kills form a link of the main range. These groups will all be found described under their own names. Not including the lateral ranges, the greatest width of the Appalachian chain is about 100 m. This is in Pennsylvania and Maryland, about midway of its course. Its extreme length is about 1,300 m.

At either end its termination is not well defined, the mountains sinking away and being lost in the hilly country that succeeds to them, and at the south its gneissoid and other ancient rocks gradually disappearing beneath the cretaceous formations of this region. In all their extent the Appalachian mountains are remarkable, not for their great elevation, nor for their striking peaks, nor for any feature that distinguishes one portion of them from the rest, but for a singular uniformity of outline, par-ticularly of that which defines the summit of the ridges, as well as that which marks their direction. While varying little in height, the ridges pursue a remarkably straight course, sometimes hardly diverging from a straight line for a distance of 50 or 60 m., and one ridge succeeding beyond another, all continuing the same general course in parallel lines, like successive waves of the sea. As one curves round into a new direction, all curve with it. Thus the valleys between the ridges preserve a uniform width, and are as remarkable for their parallelism as are the hills which bound them.

An able paper upon "The Physical Structure of the Appalachian Chain" was read before the American association of geologists and naturalists in 1S42, by the Profs. Rogers, who were at the head of the geological surveys of Pennsylvania and Virginia, and who had extended their observations into the continuations of the chain N. and S. from these states. This paper is still the most complete treatise upon this subject. Prof. Guyot has also given much attention to the physical structure of these mountains, and made careful barometrical measurements of several of their highest summits, both near their northern and southern extremities. - The general course of the Alle-ghanies is that of the coast line opposite to them. The sea makes its nearest approach to them at the mouth of the Hudson river, which is only 50 m. from the passage of this river through the Highlands. Thence as far 8. as Cape Hatteras, the width of the Atlantic slope gradually increases, till the space between the coast and the Blue Ridge is about 200 m.; and so it continues to the southern extremity of the mountains. This space is a hilly district, gradually becoming of higher elevation as it extends back from the coast.

In New England its average height at the base of the mountains is about 500 ft. above the sea; in Pennsylvania, 300; in Virginia, 500; and further S. 1,200. From the mountains to the lowest falls of the streams over the edge of the granitic platform, this is for the most part a region of the lowest stratified, metamorphic, and granitic rocks. These lowest falls mark the head of navigation of the streams, and the descent to the lower and more level platform of the upper secondary and tertiary formations, which in the southern states stretch along the coast in a belt sometimes reaching 100 m. in width. The eastern ridges of the chain, rising from their elevated base, do not present the appearance of the height above the sea which they actually reach; and on their western slope, which stretches far away toward the Mississippi, their height is still more completely lost in the elevated and wide-spread plateau. Between Lake Champlain and Lake Ontario, this western table land is 1,500 ft. above the sea, and from it as a base rise the high summits of the Adirondack mountains. In Virginia and Tennessee, as observed by Prof. Guyot, the bottom of the valley W. of the Alleghanies is from 1,000 to 2,000 ft. above the sea, and beyond it for 100 m.

W. extends a plateau of 1,500 to 2,000 ft. elevation, traversed by longitudinal ridges. All the cross sections from the eastern edge of the granite present first the slightly undulating profile of the Atlantic slope, which is succeeded by the sudden rise to the highest elevation, and this by the wave-like descent and ascent across the valleys and the ridges, and finally terminate in the gradual descent on the western table land. As first pointed out by Prof. Rogers, the same law is found to obtain in this chain and in the Jura mountains, of steepest general slopes toward the east; but of individual ridges the gentler slopes are toward the east, and the steepest inclinations toward the west. In the mid-region of the chain - in New Jersey, Pennsylvania, and Maryland - where the breadth is greatest, the height appears to be correspondingly diminished. The summits, valleys, and table land all reach here their least elevation. The highest summits are but little over 2,000 ft. above the sea. Still the barrier between the eastern and western waters is complete; and no clean cut through the range is anywhere found, excepting that of the Mohawk river in New York, the highest elevation of which is only 400 ft. above the sea.