40. =The Oases.=--The chief oases[6] of the Libyan desert--Dakhla, Kharga, Baharia and Farafra,--occupy extensive depressions cut down through the horizontal Eocene strata[7] to the underlying saddle of Cretaceous rocks; some of the more porous beds of the latter are water-bearing and from them, either through natural passages or through artificial borings, the water rises to the surface, often under considerable pressure. The floor level varies considerably but the cultivated lands in general lie between 70 and 115 metres above sea level. [6] See Geological Survey reports, P.W.M., Cairo. [7] With the exception that Dakhla is almost entirely cut out in Cretaceous strata. 41. =Dakhla oasis.=--This, by far the most important and prosperous of the Egyptian oases, lies three days’ march west of Kharga, or about 300 kilometres due west of Armant in the Nile valley. The site is a depression lying at the foot of the great east and west Cretaceous escarpment, bounded to the south by the undulating desert of Nubian sandstone, which stretches unchanged almost to the heart of the continent. The inhabitants of Dakhla, numbering over 17,000, are distributed among 12 villages and form a practically self-supporting community. The cultivable land within the oasis (400 square kilometres) amounts to nearly 50,000 acres, of which one half is under cultivation; in addition several extensive areas of alluvium covered ground exist outside the oasis proper, notably on the Gabbari road between Dakhla and Kharga. Owing to the difficulty of drainage, salines, saltyland, marshes and pools occupy some 7,000 acres. There are nearly 130,000 adult palm trees in Dakhla, a large export trade in dates being carried on with the Nile valley; the finest crops of wheat and barley are raised, while the fruits of the oasis, oranges, apricots, mulberries, etc., are abundant and of excellent quality. Taxes are levied as follows:--(1) Mature date-palms are taxed 1¹⁄₂ piastres each per annum; (2) Modern wells (i.e. biyâr, made with the existing boring plant) pay 50 piastres per annum per qirat of water; (3) Ancient wells (aiyûn) pay the same, except that in some cases those used for irrigating palmgroves are exempt. There are 7¹⁄₂ trees and 1¹⁄₂ acres per inhabitant, and the total tax paid by the community is about £E. 2,500.