464 AETESIAN WELLS IIST THE DESERT. 



wellis have lately been employed in Algeria for a purpose which 

 has even now a substantial, and may hereafter acquire a very 

 great geographical, importance. It was observed by many earlier 

 as well as recent travellers in the East, among whom Shaw de- 

 serves special mention, that the Libyan desert, bordering upon the 

 cultivated shores of the Mediterranean, appeared in many places 

 to rest upon a subterranean lake at an accessible distance below 

 the surface. The Moors are vaguely said to lore artesian wells 

 down to this reservoir, to obtain water for domestic use and irri- 

 gation, and there is evidence that this art was practiced in ISTorth- 

 em Africa in the Middle Ages. But it had been lost by the 

 modem Moors, and the universal astonishment and incredulity 

 with which the native tribes viewed the operations of the French 

 engineers sent into the desert for that purpose, are a sufficient 

 proof that this mode of reaching the subterranean waters was 

 new to them. They were, however, aware of the existence of 

 water below the sands, and were dexterous in digging wells — 

 square shafts hned with a framework of palm-tree stems — to the 

 level of the sheet. The wells so constructed, though not tech- 

 nically artesian wells, answer the same purpose ; for the water 

 rises to the surface and flows over it as from a spring.* 



A reply to this article "will be found in Viollet, Theorie des Putts Artesiens, 

 p. 217. 



In some instances the water has rushed up with a force which seemed to 

 threaten the inundation of the neighborhood, and even the washing away of 

 much soil ; but in these cases the partial exhaustion of the supply, or the relief 

 of hydrostatic or elastic pressure, has generally produced a diminution of the 

 flow in a short time, and I do not know that any serious evil has ever been 

 occasioned in this way. 



In April, 1866, a case of this sort occurred in boring an artesian well near 

 the church of St. Agnes at Venice, "When the drill reached the depth of 160 

 feet, a jet of mud and water was shot up to the height of 130 feet above the 

 surface, and continued to flow with gradually diminishing force for about 

 eight hours. The removal of the sand brought up by the water undermined 

 the superficial strata of the earth, and thus caused a subsidence which cracked 

 the walls of houses. — Omboni, Le Nostre Alpi, 1879, p. 452. 



* See a very interesting account of these wells, and of the workmen who 

 clean them out when obstructed by sand brought up with the water, in 

 Laurent's memoir on the artesian wells recently bored by the French Govern- 

 ment in the Algerian desert, Memoire sur le Sahara Oriental, etc., p. 19, et 

 seg. Some of the men remained under water from two minutes to two min- 

 utes and forty seconds. Several officers are quoted as having observed im- 

 mersions of three minutes' duration, and M. Berbrugger witnessed one of six 



