TOPOGRAPHY. 17 



ous in the lower portion. Here and there, but forming onh' a small 

 fraction of the entire area, are oases, watered b}^ springs and wells, 

 where groves of date palms flourish. 

 Schirmer'^' gives a graphic description of the Sahara. He writes: 



The desert, more than any other part of the surface of the globe, has the appear- 

 ance of immobihty. The iuijjlacable climate has depopulated the land. The great 

 I)lains have an aspect of absolute emptiness. The mountains are like skeletons from 

 M-liich the sun has devoured the flesh. The dunes look like solidified waves of dull 

 gold. The absence of sound is such that, as one traveler has put it, "One hears the 

 silence." Everything appears unchangeably fixed in the intense light. 



Pomel estimates that only about one-ninth of the total area of the 

 Sahara is covered with sand dunes. The higher dunes occur in more 

 or less regular chains, which have often been likened to the waves of the 

 sea, caught and petrilied. These sand hills sometimes reach a height 

 of 1,000 feet. Smaller dunes, very regular in their rounded outline, 

 often cover extensive areas, as, for example, between Biskra and the 

 Melrirh Chott. Dunes of this character are generally formed by vari- 

 ous desert shrubs and her))s that are able to send up new shoots 

 through the sand which drifts over them from time to time, thus con- 

 tinuall}^ raising the height of the dune. The largest sand hills are 

 often formed about rocks and clitl's, which arrest the driftino- ,sand. 

 The soil of the dunes is a fine and remarkabl}' homogeneous sand. 



Contrary to the general notion, the larger dunes are not continually 

 shifting their position, but are suiBcientl}^ permanent features of the 

 landscape to have received in many cases names that are handed down 

 by the Arabs from generation to generation. For this reason, and 

 because drinkable water and vegetation are more apt to occur near the 

 dunes than elsewhere, the caravan routes in the Sahara follow the 

 dunes wherever possible. 



In western Algeria the desert is high. Hills and mountains of sun- 

 scorched rock, with smooth surfaces and sharp, unworn edges, rise out 

 of stony plains. Jagged cliffs, often of the most fantastic form, stand 

 sentinel over the deep canyons and gorges that have been cut out by 

 occasional torrents. Oases are few and far between. This is, indeed, 

 the most barren and inhospitable part of the desert. 



Toward the east the altitude of the desert decreases until, near the 

 frontier of Tunis, a region of chotts, or salt lakes, lying below sea 

 level, is reached. During most of the year the bottoms of these basins 

 are dry or, at most, muddy beneath a crust of glittering white salt, 

 which gives rise to remarkable displays of mirage. But during the 

 wintei; they are partly tilled by streams that descend from the moun- 

 tains on the west and north. The eastern part of the Sahara in Alge- 

 ria is mainly flat or gently rolling. Its surface is covered with sand. 



«Schirmer, Le Sahara, p. 139 (1893). 

 28932— No. 80—05 2 



