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 of grain or vegetable. *23 [Footnote 23: Cieza de Leon, Cronica, cap. 73. The remains of these ancient excavations still excite the wonder of the modern traveller. See Stevenson, Residence in S. America, vol. I. p. 359. - Also McCulloh, Researches, p. 358.] The Peruvian farmers were well acquainted with the different kinds of manures, and made large use of them; a circumstance rare in the rich lands of the tropics, and probably not elsewhere practised by the rude tribes of America. They made great use of guano, the valuable deposit of sea-fowl, that has attracted so much attention, of late, from the agriculturists both of Europe and of our own country, and the stimulating and nutritious properties of which the Indians perfectly appreciated. This was found in such immense quantities on many of the little islands along the coast, as to have the appearance of lofty hills, which, covered with a white saline incrustation, led the Conquerors to give them the name of the sierra nevada, or "snowy mountains." The Incas took their usual precautions for securing the benefits of this important article to the husbandman. They assigned the small islands on the coast to the use of the respective districts which lay adjacent to them. When the island was large, it was distributed among several districts, and the boundaries for each were clearly defined. All encroachment on the rights of another was severely punished. And they secured the preservation of the fowl by penalties as stern as those by which the Norman tyrants of England protected their own game. No one was allowed to set foot on the island during the season for breeding, under pain of death; and to kill the birds at any time was punished in the like manner. *24 [Footnote 24: Acosta, lib. 4, cap. 36. - Garcilasso, Com. Real., Parte 1, lib. 5, cap. 3.]