ARTESIAN WELLS IN THE DESERT. 479 
wells 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 ear- 
lier as well as recent travellers in the East, among whom Shaw 
deserves 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 dore artesian 
wells down to this reservoir, to obtain water for domestic use 
and irrigation, and there is evidence that this art was practised 
in Northern Africa in the Middle Ages. But it had been lost 
by the modern Moors, and the universal astonishment and inere- 
dulity 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 dig- 
ging wells—square shafts lined with a framework of palm-tree 
stems—to the level of the sheet. The wells so constructed, 
though not technically artesian wells, answer the same purpose ; 
actually shown to have happened. In an article in the Annales des Ponts et 
Chaussées for July and August, 1839, p. 131, it was suggested that the sinking 
of the piers of a bridge at Tours in France was occasioned by the abstraction of 
water from the earth by artesian wells, and the consequent withdrawal of the 
mechanical support it had previously given to the strata containing it. A 
reply to this article will be found in VioLueT, Théorie des Puiis Artésiens, 
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 occa- 
sioned 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 180 feet above the 
surface, and continued to flow with gradually diminishing force for about eight 
hours. 
