3 dip away from No. 1. No. 4 and C are generally nearly horizontal, except in the vicinity of mountain disturbances. Now, by keeping in mind the dips of the several strata, and tracing each, in conception, underneath those which cover it, the reader will be able to present to his imagination a sort of stereoscopic view of the underground structure of the Northern States. I have now-leaving out of the account the debatable Marshall-barely enumerated the epochs of two great periods of the world's organic history, the Silurian and Devonian. Who has considered the measureless intervals which have been so glibly hurried over-the rising and setting suns, the passing tempests, the lonely-budding tree, the sands worried to and fro upon the uncertain beach, the lives of myriads of conscious forms in a long succession of populations, the heaving shore, the rise of continents, the burial of beautiful but senseless ruins beneath acres of sediments from which they shall never be exhumed? Let me commend the sublimity of the theme to the reader's attention. We are now on the threshold of another great period of the world's history. Graceful tree-ferns are waving in the distance, and giant club-mosses are uttering from their fronds a breezy murmur refreshing to the mind wearied with the contemplation of the uncouth and sombre forms which vegetated in the earlier seas. Looking through the vistas of the future, we behold lazy reptiles reposing upon banks protected by the tangled stems of lepidodendra and calamaria, or floating in the tepid bayous of a tropical jungle. The novelty and interest of the prospect invite us onward, but the vastness of the field bids us pause and refresh ourselves before we venture upon our jottings from the scenes of the Carboniferous Period. FOU CHAPTER XIII. AN UNDERGROUND EXCURSION. OUR hundred feet beneath the foundations of the city, with its piles of brick, and marble, and iron-beneath the roots of the oaken forest and its Dodonean colonnades -beneath the bed of the flowing river and its freight of animated hulls-down four hundred feet beneath the light of the nineteenth century, guided only by the glimmer of the oil lamp suspended from his smutty cap, the miner works the coal which blazes in the cheerful grate, or wakes the slumbering energy which drives the monster steamer on the stormy wave. Let us enter the yawning avenue to this subterranean world. [See Appendix, Note V.] Armed each with a miner's lamp, and clad in a miner's garb borrowed for the occasion, we step upon a platform, or "cage," six feet square, suspended by iron rods connected with machinery moved by an engine, and, at the word, begin to sink into the gulf of blackness beneath us. This perpendicular hole, perhaps eight feet square, is called the "shaft." By the light of the outer world thrown into the mouth of the chasm, we perceive that the shaft passes at first through a few feet of sand and gravel. Lower down the darkness of the pit enshrouds us, but we learn by the gleam of the lamps that we are passing through fifty feet of coal-black shales, which, like the sandy beds above, are held in their places by a frame of planks. We next find ourselves in the middle of an aperture through a bed of limestone perhaps twenty-five feet thick. The walls are |