262 THE MEDITERRANEAN, PHYSICAL AND HISTORICAL. 



interpreted. It has boeu abiiudaiitly proved by the researches of travel- 

 lers and geologists that such a sea was ueitlier the cause nor the ori- 

 gin of the Libyan Desert. 



Rainless and sterile regions of this nature are not peculiar to north 

 Africa, but occur in two belts which go round the world in either hem- 

 isi)here at about similar distances north and south of the e(j[uator. 

 These correspond in locality to the great inhind drainage areas from 

 which no water can be discharged into the ocean, and which occupy 

 about one-fiftli of tlie total land surfai^e of the globe. 



The African Sahara is by no means a uuiform plaiu, but forms sev- 

 eral distinct basins containing a considerable extent of what may 

 almost be called mountain land. The Hoggar Mountains, in the center 

 of the Sahara, are 7,000 feet high, and are covered during three months 

 with snow. The general average may be taken at 1,500. The physi- 

 cal character of the region is very varied; in some places, such as at 

 Tiout, Moghrar, Touat, and other oases in or bordering on Morocco, 

 there are well watered valleys, with fine scenery and almost European 

 vegetation, where the fruits of the north flourish side by side with the 

 palm tree. In others there are rivers like the Oued (xuir, an aifluent of 

 the Niger, which the French soldiers, who saw it in 1870, compare to 

 the Loire. Again, as in the bed of the Oued Rir, there is a subterra- 

 nean river, which gives a sufficient supply of water to make a chain of 

 rich and well-peopled oases equal in fertility to some of the finest por- 

 tions of Algeria. The greater part of the Sahara, however, is hard and 

 unduUiting, cut up by dry water courses, such as the Igharghar, which 

 descends to the Ohott Melghigh, and almost entirely without animal or 

 vegetable life. 



About one sixth of its extent consists of dunes of moving sand, a 

 vast accumulation of detritus washed down from more northern and 

 southern regions — perhaps during the glacial epoch — but with no indi- 

 cation of marine formation. These are difticult and even dangerous to 

 traverse; but they are not entirely destitute of vegetation. Water is 

 found at rare but well-known intervals, and there is an abundance of 

 salsolaceous plants which serve as food for the camel. This sand is 

 largely produced by wind action on the underlying rocks, and is not 

 sterile in itself; it is only the want of water which makes it so. 

 Wherever water does exist or artesian wells are sunk oases of great 

 fertility never fail to follow. 



Some parts of the Sahara are below the level of the sea, and here are 

 formed what are called chotts or sebkhas, open depressions without out 

 lets, inundated by torrents from the southern slopes of the Atlas in 

 winter, and covered with a saline efflorescence in summer. This salt by 

 no means proves the former existence of an inland sea; it is produced 

 by the concentration of the natural salts, which exist in every variety 

 of soil, washed down by winter rains, with which the uuevaporated res- 

 idue of water becomes saturated. 



