Most of these beneficent works of the Incas were suffered to go to decay by their Spanish conquerors. In some spots, the waters are still left to flow in their silent, subterraneous channels, whose windings and whose sources have been alike unexplored. Others, though partially dilapidated, and closed up with rubbish and the rank vegetation of the soil, still betray their course by occasional patches of fertility. Such are the remains in the valley of Nasca, a fruitful spot that lies between long tracts of desert; where the ancient water-courses of the Incas, measuring four or five feet in depth by three in width, and formed of large blocks of uncemented masonry, are conducted from an unknown distance. The greatest care was taken that every occupant of the land through which these streams passed should enjoy the benefit of them. The quantity of water alloted to each was prescribed by law; and royal overseers superintended the distribution, and saw that it was faithfully applied to the irrigation of the ground.20 The Peruvians showed a similar spirit of enterprise in their schemes for introducing cultivation into the mountainous parts of their domain. Many of the hills, though covered with a strong soil, were too precipitous to be tilled. These they cut into terraces, faced with rough stone, diminishing in regular gradation towards the summit; so that, while the lower strip, or anden, as it was called by the Spaniards, that belted round the base of the mountain, might comprehend hundreds of acres, the upper-most was only large enough to accommodate a few rows of Indian corn.21 Some of the eminences presented such a mess of solid rock, that, after being hewn into terraces, they were obliged to be covered deep with earth, before they could serve the purpose of the husbandman. With such patient toil did the Peruvians combat the formidable obstacles presented by the face of their country! Without the use of tools or the machinery familiar to the European, each individual could have done little; but acting in large masses, and under a common direction, they were enabled by indefatigable perseverance to achieve results, to have attempted which might have filled even the European with dismay.22 In the same spirit of economical husbandry which redeemed the rocky sierra from the curse of sterility, they dug below the arid soil of the valleys, and sought for a stratum where some natural moisture might be found. These excavations, called by the Spaniards hoyas, or "pits," were made on a great scale, comprehending frequently more than an acre, sunk to the depth of fifteen or twenty feet, and fenced round within by a wall of adobes, or bricks baked in the sun. The bottom of the excavation, well prepared by a rich manure of the sardines,--a small fish obtained in vast quantities along the coast,--was planted with some kind or grain or vegetable.23