_Geographical distribution._--This rock occurs extensively along all the north-western side of the primitive of the great chain of the Alleghanies. In lower Canada and Vermont, it is accompanied by granular limestone and granular quartz, which separate it from the mica slate and talcose rocks on the east. [See Eaton's Index to the Geology of the Northern States.] It is there usually inclined towards the west, at an inconsiderable angle. It is separated from the compact fletz limestone of the valley of Lake Champlain by a stratum of old red sandstone, which forms {325} the upper part of a range of hills, called, in Vermont, the Snake mountain. In Berkshire county, in the western part of Massachusetts, and along the eastern side of the Hudson in New York, a stratum of primitive clay-slate intervenes between this rock and the granular limestone. The New Lebanon mountain, which is of slate, and divides the primitive limestone of Pittsfield, Richmond, Stockbridge, &c. from the transition which occurs at New Lebanon springs, and along the western base of this range, is considered primitive. (_Dewey in Silliman's Journal._) To the north-east of the Hudson river, the transition limestone nowhere occupies any great extent of surface from east to west, but is a narrow strip running along the margin of the primitive, and in a few miles is succeeded either by red sandstone, or clay-slate resting upon it. In Vermont, in the same neighbourhood, it alternates with clay-slate, and supports red sandstone. Crossing the Hudson above the highlands, and proceeding south-west, little of this stratum is seen in the lower part of New York; but it becomes more abundant in the western parts of New Jersey and Pennsylvania. If we suppose the whole of the Alleghany mountains of Pennsylvania, Maryland, and the western parts of Virginia, removed to a level with the surface at base of their eastern declivities, it is probable their foundation, which would be thus exposed, would be found through their whole extent to be of transition limestone. This rock is almost the only one which occurs between the primitive limestone. About twenty miles west of Philadelphia and Harrisburgh, Cove Hill, the North and South mountains, and the other eastern ranges of the Alleghany, are all based upon metalliferous limestone. It is seen emerging from beneath the sandstone which forms the body of these mountains at O'Connel's town, and in most of the vallies between the Alleghanies. We learn from Maclure, that it extends itself to the south and west, nearly to the termination of this range of mountains at the {326} confluence of the Alabama and Tombigbee rivers in Mississippi.