The intricate passages branching out into a mysterious distance; the vaults and high halls faintly illumined here and there by a glimmering lamp; the dark forms emerging every now and then from some obscure recess, and then again plunging into night, like demon shades; the clanking of hammers, the rushing of waters, the creaking of wheels, the monotonous sound of machinery, or the loud explosion which, repeated by subterranean echoes, rolls like muttering thunder from vault to vault, the oppressive air in the low galleries, through which he can only move in a stooping position; the fear of being crushed any moment by a falling rock, or shivered to atoms by fire-damp combustion,—all combine to produce an impression which can seldom be made by any scenes above ground. The admiration which this imposing spectacle necessarily calls forth in his mind increases when he reflects how much skill and experience was required, and how many improvements and inventions had to be made, before mining could be brought to its present state of perfection. Ores sometimes occur, like coal, in layers or beds, running parallel with the strata of the inclosing rocks, or in prodigious irregular masses. Most commonly, however, they are found in veins traversing the rocks in every conceivable direction, and filling the crevices and chasms which former terrestrial revolutions have rent in the hard stone. From the wild and titanic powers that have here been at work, it may easily be imagined how irregular the direction of these veins must be, and under how many various forms they must appear. Here they are horizontal, there vertical; here they form thin layers, there they fill chasms several hundred feet thick. Sometimes they split into several minor branches, or make abrupt bends, and frequently they have been rent, torn, or displaced in every possible manner by subsequent revolutions. Their length is as various as their thickness or their direction. Some are short, while others traverse the rocks to a distance of many miles. Thus the argentiferous veins in the neighbourhood of Clausthal, in the Harz, are three leagues long, and the famous Veta Madre, or chief lode of Guanaxuato in Mexico, has been traced for a length of eight miles. With regard to depth, the lower extremity of hardly a single mineral bed or vein of any note has as yet been pointed out, though many have been worked to a considerable depth. Thus, one of the pits of St. Andreasberg, in the Harz, is 2,485 feet deep, though, on account of its high situation in the mountains, not much more than 280 feet below the surface of the sea, while, in the coal mines of Valenciennes and Liège, the deepest shafts are sunk from 1,300 to 1,600 feet below the level of the ocean. The shaft of the colliery of Sacrée Madame, near Charleroi, is 800 yards deep, and that of Dukinfield Colliery 2,050 feet.