At Pica, on the piedmont slope to one side of the stream courses, tunnels have been built into the piedmont deposits and carry the water by low gradients down to the intake of the pipes and canals that distribute it. We rode up to the intake of one of these (La Vertiente del Resbaladero) and saw the pool at the foot of cliffs partly encircling a cavelike opening. It was at that time the chief point of interest in the town. A similar system of water recovery has been built in the desert places of other countries. In Persia such a subterranean conduit is called kanat, in Baluchistan and in Turkestan kariz. In Tidi- kelt and other provinces of the Algerian Sahara it is called fog- gara, and all who have worked to increase its yicld have a share in the flow. A recent account has been given of the pits and connecting galleries called rétharas in Morocco.’ A great water tunnel over a mile long has been built near a dry stream bed close to the Khojak Pass in India; and southern California has a number of like tunnels, some with ‘‘weep holes’ where the water discharges into the main opening.*
The entire system of galleries or tunnels at Pica is one of great variety of structure and flow, and | know of no other town in South America that has so many of them or that depends so completely upon the artificial recovery of the ground water for both its drinking water and its irrigation. The galleries have been cut in a soft sandstone which is yet sufficiently hard to stand up under its own weight and to sup- port a roof of the same material. Only in certain places in a few galleries is a small amount of timbering or stonework nec- essary. Some are lighted for a part of their length and care- fully kept up, others are dark and interrupted here and there by falls of sand or soft rock from the roof or the somewhat overhanging upper walls. From the largest gallery, the Galeria Comima, water is supplied at the rate of more than one and a half liters a second; but its earlier rate was four liters a second, the decrease being due to the failure of the owners to keep the floor clear and the intake sufficiently open. Some of the galler-
7 Pierre Troussu: Les rétharas de Marrakech, France-Maroc, Vol. 3, 1919, pp. 246- 240.
fA. PL Davis and H. M. Wilson; Urrigation Engineering, 7th edit., New York, 1919, Pp. 50
