earth's crust has cracked the shaly roof; the opposite sides of the fissure have been moved to and fro over each other, and under the mighty pressure the two opposing faces have been beautifully polished.

But probably different sights will greet our eyes. The rocky ceiling is ornamented every where by the most exquisite tracery-inim

itable representations of the delicate fronds of ferns (Fig. 64). We remove a scale of the rock, and behind is still another picture. Remove a second, and from the dark black rock gleams forth another form of grace and beauty. The whole mass of the shaly roof is a portfolio of inimitable sketches. The sharpest outlines and minutest serratures of the leaves are clearly traced. The very nerves, with their characteristic bifurcations, are accurately depicted on this wonderful lithograph. Petioles, and buds, and woody stems, and

cones, and fruits, slender grass-leaves, striated rushes, the

fluted stems of gigantic club-mosses, the scarred and pitted trunks of extinct tree-ferns, diversify, by turns, the crayon sketchings of the dusky ceiling. Prostrate, all! They have stood erect; the soil has held them by their spreading roots, the genial sunlight has warmed them, the vital breeze has fanned their verdant foliage; change, which transforms all things, has swept over them, and graceful fern and giant club-moss, slender reed and arrogant conifer, have laid down together in their couch of sediment, and the old sexton, Time, has piled upon them the accumulated ashes of a hundred succeeding generations of trees, and herbs, and perished populations. What a store-house of suggestions is here! The dusty "Catacombs" are less eloquent in their inscriptions; the vaults of the Pyramids recite a history less full of meaning. To the soul that holds communion with the visible ideas that dwell about him, these rocky walls are vocal with narratives of earthquake and flood, of nodding verdure and of desolating surge; these shales are the tombstones of generations, on which are inscribed chronologies whose minutes are the cycles of the Hindoo. Here is the populous abode of world-ideas. Through these dim avenues flit spectres of the ancient thoughts which were once the acting energies of our planet. Here is the real Acherontian realm. He who has descended to these subterranean halls, and held converse with the forms which here abide, has visited a world and communed with intelligences of which Anchisiades had only dreamed.

Shall we venture to translate the histories recorded upon these rocky leaves? What were the scenes and events of that epoch of the world when these buried vegetable forms were living, growing organisms, and Nature was storing away for the human race these magazines of fuel ?

IT

CHAPTER XIV.

THE SCENERY OF THE COAL PERIOD.

T was in the middle ages of the history of the world. The growing continents had lifted their brows above the surface of the all-embracing sea; but their spreading plains and long-extended shores were still the empire of the garpikes, and the nursery of illimitable beds of encrinites and polyps. The Gulf of Mexico jutted northward to Middle Iowa, and rolled its widening waters northwest far toward the sources of the Missouri River. There are good reasons for believing that it stretched through the entire length of the continent to the Frozen Ocean. The shoreline of the Atlantic reached from Connecticut through Southern New York and Northern Ohio, Indiana, and Illinois, to the valley of the future Mississippi. All the centre of Michigan was a sea-bottom, and not unlikely a gulf projected northward over the peninsula now inclosed by the great lakes. There was never, however, any free communication between the Michigan Gulf and the ocean after the later portion of the Devonian Age. Hudson's Bay stretched far toward the site of Lake Superior, as the Arctic Sea pushed down from the north to fall into the warm embrace of the waters of the Mexican Gulf. The great lakes were not-save, perhaps, Lake Superior-nor the mighty Mississippi, nor the thunder-voiced Niagara. The youthful continent was yet unclothed with soil, save the rocky detritus which nourished the lean vegetation which began to garnish the land during the period of the Chemung and Marshall. The skeleton rocks protruded every

where in bleak, inhospitable exposures. Occasionally in a low valley was gathered a cluster of dwarfish trees, nourished by the crude aliment, of a hastily-compounded soil. Beast, and bird, and insect were yet slumbering in the

chambers of the future-ideas reserved in the all-producing mind of Omniscience. Food for them there was none. The atmosphere was a noxious poison, charged with all the carbon which now exists in the form of modern vegetation and beds of mineral coal. Denizens of the sea had for ages strewn its bottom with the ruins of their workmanship-mountains of coral masonry had been reared by the little polyp architect, but in all the murky air which floated over the land and sea was not one motion of an animated being-not a voice-no song of bird, or hum of insect's wing to break the dread, eternal silence. The surges broke upon the beach, the tempest gathered in the thickening air, but no beast hurried to the sheltering cave; the storm burst upon the bald and desolate cliff, but no fluttering wing sought protection from its fury.

The period had now arrived, however, when this verdureless and voiceless scene was to be clothed and animated. Now was perhaps the most important-epoch in the whole physical history of our planet. The forces of nature were now to be called to their grandest exercise. The laws of chemistry were summoned to an operation miraculously beneficent and providential. Organic force now girded itself for the production of new and higher forms of animalization, and for the display of the earliest and richest exuberance of the vegetable kingdom.

The series of animate existences began with the protozoon, and had been carried through long progressive stages to the highest types which make their home in the water and respire that element. Man, the far-off consummation of all these improvements, was to be a vastly superior being; but the next step in the direction of this consummation must be the introduction of an air-breathing animal. In the existing condition of the world no air-breathing animal could survive, and Nature was called upon to