The southern slope of this porphyritic range is crossed by the famous Veta Madre of Guanaxuato, the richest silver lode as yet discovered in Mexico. This enormous vein, which traverses the country for upwards of eight miles, with an average width of from 120 to 135 feet, is, however, not productive throughout its whole extent, but the ore occurs in branches and bunches, leaving intermediate spaces of dead and unproductive ground. Among the numerous mines that have been opened along its course, the Valenciana exhibited, at the beginning of the present century, the almost unparalleled example of a mine which, during a period of more than forty years, never yielded its proprietors less than an annual income of from 80,000_l._ to 120,000_l._ The part of the Veta in which it is situated had remained unexplored till 1760, when Obregon, a young Spaniard, began to work it, with the assistance of some friends who advanced him the necessary capital. In the year 1766 the diggings had reached a depth of 240 feet, and the expenses were far greater than the proceeds. But Obregon clung with the passionate ardour of a gambler to the hazardous enterprise on which he had staked all his hopes of fortune. In 1767 he entered into partnership with a small shopkeeper, Otero, who was destined soon to share the fabulous riches that were about to reward his perseverance. Already in the following year the produce of the mine considerably increased, and in 1771 it began to yield enormous masses of sulphuret of silver. From that time till 1804, when Humboldt left Mexico, it never produced less than 560,000_l._ worth of silver annually, and the net profits of the partners amounted in some years to 240,000_l._ Under the title of Conde de la Valenciana, Obregon maintained the simple habits and the urbanity of character which had distinguished him in poverty. When he began to work his mine, the goats were feeding on the spot where ten years later a thriving town of 8,000 souls had started into existence. Guanaxuato, the capital of the State of the same name, is indebted to the neighbourhood of the richest silver mines in the world for its origin and prosperity. Inclosed in a narrow valley, its houses rise in terraces one above the other; and the contrast of the magnificent abodes of the rich mining proprietors with the miserable huts of their dependants adds to the singular appearance of the place. The Mexican miner is, however, not so poor as his wretched dwelling might lead us to suppose. In some measure he shares the fortunes of the proprietors of the mines, as he is entitled to part of the ore; so that when the vein is more than usually productive his weekly profits may amount to as much as a hundred dollars. Yet he never thinks of purchasing a piece of land, or of repairing his hut, when favoured by fortune; but foolishly squanders his money in drinking and gambling, and seldom returns to his work before his last farthing has been spent.