536 THE POPULAR SCIENCE MONTHLY. 



tains an elevation of over four thousand feet. The journeys of Barth 

 and Yogel discovered that, at a short distance south of Tripoli, a series 

 of terraces lead gradually to the vast plains of the desert, where there 

 are only moderate undulations with occasional ravines and isolated 

 masses of rock to Soodan. The southern part of the route was over 

 plains slightly inclined southward. The greatest height observed in 

 that region was six hundred metres. 



M. Dupouchel, Ingenieur en chef des Fonts et Chaussees, went in 

 1877 to examine the ground west of the Ahaggad, and study the prac- 

 ticability of opening a railway between Algeria and the valley of the 

 Niger of Soodan. The results of his examinations have appeared in 

 book form, accompanied with maps and drawings. The route that he 

 recommends commences at Algiers, and passes by Afreville, Boghari, 

 Laghouat, and the oases of Touat, finally striking the Niger at Bamba, 

 a short distance east of Timbuctoo. An eastern branch would descend 

 that river to longitude 2° east, and would run from there toward the 

 Tchad Lake. A western branch would ascend the Niger as far as 

 Kouma, and then run to Saint-Louis, The total length of the line 

 from Algiers to the Niger, deducting the part already constructed to 

 Afreville, would be about 1,700 miles, of which the total cost is esti- 

 mated at 400,000,000 francs (about $77,000,000). This is 115,000 less 

 per mile than the average of all the railroads built in the United States 

 during the year 1874, and $60,000 less per mile than the cost of the 

 Central Pacific. President Grevy has recently been written to, and 

 urged to appoint a commission to examine a proposal to construct that 

 railroad. 



It will readily be seen what an important element in the construc- 

 tion of a railway will be the power to supply water from underground 

 as the work progresses. But there are enthusiasts who maintain that 

 the object now to be accomplished is not simply the establishing of 

 communication across the desert, nor the submerging of one very 

 small portion for the benefit of another small portion, but no more nor 

 less than the reclaiming — the fertilization — of the whole Sahara. This, 

 indeed, sounds rash, and yet no less an authority than Gerhard Rohlfs, 

 who has explored greater areas of Sahara than any other European, and 

 whose journey from Tripoli to Rhadames and Fezzau won him a gold 

 medal from the Royal Geographical Society of London, sustains the 

 idea by saying that Nature would soon begin to assist man in the 

 herculean undertaking. According to this traveler, three distinct zones 

 separate the center of the desert from the neighboring lands of the 

 Tchad Lake in the south ; in the third or northernmost of these are im- 

 mense forests of mimosas, where the ground is characterized by the 

 absence of the smallest stone, and which, according to the aborigines, ex- 

 tend from Egypt to Timbuctoo, covering the Kordof an, the Darf oor, the 

 Kamen, and the country of the Touaregs. Professor Rohlfs advances 

 the theory that these forests are encroaching on the desert, and that in 



