References: Modern.—a, the Atlantic sea; b, recent or cretaceous formations; c, granitic and volcanic; d, mesozoic, new red, &c.; e, metamorphic, gneissic, &c.; g, sandstones and limestones of the valley, or the lower palæozoic formations; h, slates and shales of the oil-producing formations; i, sandstones overlying the oil strata, including the old red and the conglomerate; j, the anthracite coal deposits; k, Cumberland coal field; l, l, n, Alleghany coal field; m, Ohio river.

The Potsdam sandstone underlies the Auroral limestone, g, and overlies the gneiss, e, which must exist to some extent in the entire basin. The dark vertical trap formations emerge from the granite, and were the means of forming the gneiss.

Ancient.—No. 1 corresponds to a, and is the granite seacoast line, forming the volcanic boundary of the ancient sea; 2 is a deep view of the volcanic vent between the granite and the gneiss, which is formed of the vented matter; 3 is the metamorphic or early gneissic sedimentary rocks; 4 corresponds to g, and is the base of the palæozoic; 5 is the bituminous slates of the oil strata, followed by the massive sandstones of the old red, and the subcarboniferous; 6 is the ancient sea, since filled by the sedimentary deposits represented in g, h, i, j, k, l, &c.; 7, 7 is the line of volcanic vents existing in the plutonic or granitic coast line, which extends from Maine to Cuba. The form of the ancient structure