Wonderful certainly is all this—the inclosing, the consolidation, the arrangement of these remarkable substances. The sea, in the first instance, may readily and abundantly have supplied all the elements of the formation; but how collected and retained, crystallized and incrusted, layer upon layer, over the rocky bottom and volcanic inner chambers, are points still of nice geological inquiry. The celebrated salt mines of Cracow, in Poland, are wondrous operations of the art of man, into the still more wondrous products and recesses of nature. Here the entire arrangements of a city are almost perfected; the streets, marketplace, chapel, rivers, reservoirs, grottoes, and all the requirements of comfort and safety gleaming in a blaze of saline crystals. “Scoop’d in the briny rock long streets extend Their hoary course, and glittering domes ascend; Down the bright steeps, emerging into day, Impetuous fountains burst their headlong way, O’er milk-white vales in ivory channels spread, And wondering seek their subterraneous bed. Long lines of lusters pour their trembling rays, And the bright vault returns the mingled blaze.” The deposit near Cracow is worked on four different levels or stories, divided into innumerable compartments, with thousands of excavations in every direction, and descending to the vast depth of one thousand feet below the surface. The length of the several passages, in their windings and turnings, is calculated to be nearly three hundred miles; about two thousand men are constantly employed in the mining operations; and, though the operations have been carrying on for the known period at least of six hundred years, the mass of rock-salt in the locality is still of inexhaustible extent. The mines in our own land are equally remarkable after their kind, and cannot fail to interest, if not to astonish, the neophyte who ventures a descent. From the mode in which they are worked, the huge pillars left to support the roof, the thousand lights that illuminate the caverns, the reverberations from the blasting which at intervals ring through their depths, a grandeur and impressiveness are imparted to a scene which scarcely any other combination of objects could produce. And another world—a world of coal and iron—in all its magnificence and riches, lies interred under these glistering stores of lime and salt! How strangely contrasting in their qualities and structure the two formations. But except that a wise and far-seeing Providence collected and garnered up the waste and decay of both for man’s use, no principle have we to guide us when speculating on their mineral properties and arrangement—no natural law certainly, self-acting upon matter and evolving new creations of its own, organic or inorganic, to reveal His inscrutable purposes. CHAPTER III. THE OOLITIC OR JURASSIC SYSTEM—AGE OF REPTILES.