176 POPULAR SCIENCE MONTHLY. 



are a part of the great arctic " sea of ice." Beyond, however, is the 

 great plain itself, its swelling undulations hardly relieving to the eye 

 the appearance of absolute flatness which the picture offers. The 

 truth is, the Sahara presents itself in a double aspect: that of the 

 flat and sandy plain and that of the rocky ridge or mountain, the 

 Hammada. It is the Hammada that is more particularly dreaded 

 by the caravans, for among their wind-swept crags there are few 

 oases, and only the blowing sands and a relentless sun are the com- 

 panions of the foot-sore pilgrim. In many parts of the flat desert 

 traveling is moderately easy, for over long distances the surface has 

 become coated into a hard, slimy crust — a solid basement rock, one 

 may call it. Along our route of travel there were no sand dunes of 

 any magnitude, the highest perhaps scarcely exceeding fifteen or 

 twenty feet, but I was informed by the distinguished French ex- 

 plorer M. Foureaud, who was then stopping at Biskra, that beyond 

 Tuggurt they rise to the prodigious height of from twelve hundred 

 to fourteen hundred feet. This speaks even more eloquently for the 

 power of the winds than do the high-tossed sands of coral islands. 



It has become customary of late with certain text-books to state 

 that the Sahara is not so flat as it is commonly assumed to be, and 

 that it is almost everywhere torn into ridges and rents. This is, 

 however, an imperfect statement of the truth. The flat desert is 

 almost interminably flat for days or even weeks of travel, with 

 hardly a rise of a few feet for mile after mile of perspective. In 

 vain the eye searches after some special object to give it relief; it 

 does not find it, unless it be the far-off tufts of an approaching 

 oasis. Often has the desert been compared with the sea, but proba- 

 bly to most persons such a comparison, except where it stands for 

 magnitude, will be considered extreme. It is true that where the 

 surface is illumined by the weird light of the mirage it may depict 

 the presence of water with startling naturalness, but the deception 

 belongs rather to the atmosphere carried by the desert than to the 

 desert itself. I am not sure that these endless sands are truly 

 imposing; wearisome they certainly are, but at times they present 

 most exquisite pictures in the varying lights of the morning and 

 evening sun. It is then that they seem to constitute a world of 

 their own, speaking in color that belongs to them alone. We were 

 not to any extent troubled by their presence, either as an impediment 

 to travel or as freely floating discomforts in the atmosphere. 



The journey which I had projected took the course of the great 

 caravan route to Lake Tchad, passing by the deep depression which 

 is occupied by the largest cliotts of the desert, the possible reclama- 

 tion of which by the Mediterranean has been the subject of much 

 study on the part of French engineers — the dream and hope of M. 



