ALLEGANY MOUNTAINS, otherwise called tin. Alla/aches, from a tribe of Indians who live on the banks of the Apalachicola, a river which proceeds from these mountains, are a part of that extensive range which is situated between the Atlantic, the Mississippi, and tin. lakes of North America; and which runs in a direction from south-west to north-east, passing through the country of the United States, and giving origin to many rivers that flow, either into the Gulf of Mexico, or into the 'Western Ocean. As the Allegany Mountains form a principal part of the chain just alluded to, they often give their name to the whole range. This range commences in Georgia, stretches northwards and east wards through the territory of Virginia, passes on in the same directions through Pennsylvania and the nor thern counties, and terminates in the division of New Brunswick. Its whole extent, according to Pinkerton, is not less than 900 geographical miles. As it approaches its termination, the mass rises in height : the chief summits are in New Hampshire, and are reported to be nearly 8000 feet above the level of the ocean. Be sides the main ridge, however, there are several others which are collateral to it, as the Iron or Bald Moun tains, the White Oak Mountains, and the Blue Moun tains; the Cumberland Mountains forming the exterior skirt towards the north-west. The breadth of the whole is often equal to seventy miles.
It is particularly deserving of notice, that while the Allegany or Apalachian Mountains give origin to several rivers, their course is likewise broken by others which take their rise in the more level country to the west of the range, and whose channels, where they have pierced the rock, arc composed of the same hard mate rials with its other parts. This is the case with the Susquehanna and the Potowmac, which open into the Bay of Chesapeake ; and, as it is affirmed, with Iludson's River in the north. Whether the passages through which these great collections of water flow towards the Atlantic, were formed by any convulsion of nature af fecting this part of the world, (Atferson's _Votes on Cie.. ginia, App. No. 2.) or whether by the gradual disintegra tion of the mass, in consequence of the action of the fluid, it is not easy to determine ; though we think it probable, that the phenomenon is to be ascribed to the union or successive operations of both these causes.
But, in whatever way we account for it, it is mimics tiooably an appearance which merits the attention of philosophers; and which by no means harmonizes with the geographical theories, which have long been mu: iv .cd by the public. (h ) For the following account of the geognostic structure of the Allegany Mountains, the Edito• is indebted to proLssor Jameson, to whose learning and talents this work is under great obligations.
As far as we know, no sell educated mineralogist has hitherto examined the geognostic structure and re lations of this great range of mountains ; nor do we even possess any very accurate description of the grouping and shape of its individual mountains. It would ap
pea• frem notices in the Berginannisches Journal, and Journal (Its Alines, and the relations of travellers, that the rocks, of which these mountains are composed, are similar in structure and arrangement to those observed in Europe. Thus granite appears, in general, to form the central and highest parts of the groupes ; although in some particular instances it is observed on a lower level than certain newer rocks that really or apparently occupy the central and highest parts of the groupe. This appearance has been urged as an objection against the general tact, that granite forms the central and high est parts of mountain groupes. An accurate knowledge of the grouping of mountains, and of the different rock formations, however, shows us that this objection has no force ; for we find that in those instances where the granite has really a lower level than the newer rocks, that these rocks arc either overlying formations, as syenite, second porphyry, newest granite, or newest ficetz trap, or partial accumulations of newer primitive, tran,,ition, or Mertz rocks; and in those instances where the granite is only apparently lower than neighbouring rocks, the deception is caused by our confounding sub ordinate with principal mountain groupes. The granite is succeeded by a class of slaty rocks, which appears in some instances to include the whole series of princi pal, conformable, primitive formations, viz. gneiss, mica slate, and clay slate ; in others, to contain only individual members of this series, as gneiss, or clay slate. The lower parts of the range are composed of flcetz rocks, and these arc principally limestone, sandstone, and gyp sum. The limestone is the most abundant of the flcetz formations, and it contains numerous petrifactions of ani mal and vegetable bodies. The animal pctrifactions are by far the most abundant; at d of these a considera ble number of ammonites, corallites, Ste. have been de stribed. In the valleys and lower parts of this range, there are considerable tracts composed of alluvial de posits, which have been formed by the washing of de 1 ris the sides of the mountains, or by the overflow ing of rivers. The slaty primitive rocks, viz. gneiss, mica slate, and clay slate, are traversed by metalliferous repositories that contain ores of copper, lead, and sil Geography, vol. iii. p. 33. et seq. Morse's Geog. of the United Stales, p. 65. and 310. edit. 1795. Pennant's d•etic Zoology, ccxxix. Journal des itf,nes, No. 54. Whitehurst's Eng. into the State and Formation ef thc Earth. Play fair's Illust. of the Huttonian Theory. (r)