The next morning, Saturday, at six o'clock, we started again. Twenty minutes later we suddenly came upon a vast excavation. From its mighty extent I saw at once that the hand of man could have had nothing to do with this coal mine; the vault above would have fallen in; as it was, it was only held together by some miracle of nature. This mighty natural cavern was about a hundred feet wide, by about a hundred and fifty high. The earth had evidently been cast apart by some violent subterranean commotion. The mass, giving way to some prodigious upheaving of nature, had split in two, leaving the vast gap into which we inhabitants of the earth had penetrated for the first time. The whole singular history of the coal period was written on those dark and gloomy walls. A geologist would have been able easily to follow the different phases of its formation. The seams of coal were separated by strata of sandstone, a compact clay, which appeared to be crushed down by the weight from above. At that period of the world which preceded the secondary epoch, the earth was covered by a coating of enormous and rich vegetation, due to the double action of tropical heat and perpetual humidity. A vast atmospheric cloud of vapor surrounded the earth on all sides, preventing the rays of the sun from ever reaching it. Hence the conclusion that these intense heats did not arise from this new source of caloric. Perhaps even the star of day was not quite ready for its brilliant work--to illumine a universe. Climates did not as yet exist, and a level heat pervaded the whole surface of the globe--the same heat existing at the North Pole as at the equator. Whence did it come? From the interior of the earth? In spite of all the learned theories of Professor Hardwigg, a fierce and vehement fire certainly burned within the entrails of the great spheroid. Its action was felt even to the very topmost crust of the earth; the plants then in existence, being deprived of the vivifying rays of the sun, had neither buds, nor flowers, nor odor, but their roots drew a strong and vigorous life from the burning earth of early days. There were but few of what may be called trees--only herbaceous plants, immense turfs, briers, mosses, rare families, which, however, in those days were counted by tens and tens of thousands. It is entirely to this exuberant vegetation that coal owes its origin. The crust of the vast globe still yielded under the influence of the seething, boiling mass, which was forever at work beneath. Hence arose numerous fissures, and continual falling in of the upper earth. The dense mass of plants being beneath the waters, soon formed themselves into vast agglomerations. Then came about the action of natural chemistry; in the depths of the ocean the vegetable mass at first became turf, then, thanks to the influence of gases and subterranean fermentation, they underwent the complete process of mineralization.