SAND-HILLS OF THE SAHARA. 133 



us a sea which may have been solidified during a violent tempest. 

 The Dunes, or sand-hills, like waves, rise one behind another even to 

 the limits of the horizon, separated by narrow valleys which represent 

 the depressions of the great billows of the ocean, all whose various 

 aspects they simulate. Sometimes they narrow themselves into keen- 

 edged crests, or shoot upwards in pyramids, or swell into cylindrical 

 domes. Seen from a distance, these Dunes also remind us at times of 

 the appearances of the nv (or granulated snow) in the amphitheatres 

 and on the ridges which lie contiguous to the loftiest Alpine summits. 

 Their colours still further enhance the illusion. Moulded by the 

 winds, the burning sands of the desert assume the same forms as the 

 ntfvfa of the glaciers." 



Whoever has seen the Dunes on the coast of Norfolk, or more 

 particularly in Gascony, may gain a very accurate conception of the 

 Desert. The only notable differences are in the extent, which here 

 seems infinite, like that of ocean ; the purity of the heaven, which is 

 seldom sullied by a cloud ; and the colour, which is of a soft, intense 

 blue. The nature of the soil is the same ; it is a very fine, shifting, 

 silicious sand, white sometimes, like that of Fontainebleau, and 

 sometimes reddened by the presence of oxide of iron. In the Sahara 

 this sand gathers in veritable Dunes, hillocks which the wind upheaves, 

 displaces, and transforms from one day to another. Only the lettes, 

 or valleys, which in our Dunes receive the pluvial waters and preserve 

 a sufficient amount of fertility, are here just moistened by rare saline 

 infiltrations, and almost always remain in a condition of absolute 

 sterility. Nevertheless, in some localities, the presence of gypsum 

 gives the sand a certain fixity, which permits a small number of 

 plants to germinate and develop themselves. This gypsum is never 

 found but in the valleys, and never in tabular masses, as on the pla- 

 teaux, but only in crystals of various forms, penetrated by silica. 

 " You pick up a pebble," says M. Martins, " and find it to be a 

 crystal." The villages are surrounded by crenellated ramparts built 

 of crystals ; the houses which compose these villages are constructed 

 of the same materials ; and very weird and splendid is the scene pre- 



