Yet they did not attempt to penetrate into the bowels of the earth 'by sinking a shaft, but simply excavated a cavern in the steep sides of the mountain, or, at most, opened a horizonal vein of moderate depth. They were equally deficient in the knowledge of the best means of detaching the precious metal from the dross with which it was united, and had no idea of the virtues of quicksilver,--a mineral not rare in Peru, as an amalgam to effect this decomposition.22 Their method of smelting the ore was by means of furnaces built in elevated and exposed situations, where they might be fanned by the strong breezes of the mountains. The subjects of the Incas, in short, with all their patient perseverance, did little more than penetrate below the crust, the outer rind, as it were, formed over those golden caverns which lie hidden in the dark depths of the Andes. Yet what they gleaned from the surface was more than adequate for all their demands. For they were not a commercial people, and had no knowledge of money.23 In this they differed from the ancient Mexicans, who had an established currency of a determinate value. In one respect, however, they were superior to their American rivals, since they made use of weights to determine the quantity of their commodities, a thing wholly unknown to the Aztecs. This fact is ascertained by the discovery of silver balances, adjusted with perfect accuracy, in some of the tombs of the Incas.24But the surest test of the civilization of a people--at least, as sure as any--afforded by mechanical art is to be found in their architecture, which presents so noble a field for the display of the grand and the beautiful, and which, at the same time, is so intimately connected with the essential comforts of life. There is no object on which the resources of the wealthy are more freely lavished, or which calls out more effectually the inventive talent of the artist. The painter and the sculptor may display their individual genius in creations of surpassing excellence, but it is the great monuments of architectural taste and magnificence that are stamped in a peculiar manner by the genius of the nation. The Greek, the Egyptian, the Saracen, the Gothic,--what a key do their respective styles afford to the character and condition of the people! The monuments of China, of Hindostan, and of Central America are all indicative of an immature period, in which the imagination has not been disciplined by study, and which, therefore, in its best results, betrays only the illregulated aspirations after the beautiful, that belong to a semi-civilized people.