356 DESERT SANDS 



descends by a steep slope, is • a vast depression of clay and 

 Band,' but still for the most part standing high above sea- 

 level. No portion of the Upper Sahara is less than 1,800 

 feet high — a good deal higher than Dartmoor or Derby- 

 shire. Most of the Lower reaches from two to three 

 hundred feet — quite as elevated as Essex or Leicester. 

 The few spots below sea-level consist of the beds of ancient 

 lakes, now much shrunk by evaporation, owing to the 

 present rainless condition of the country ; the soil around 

 these is deep in gypsum, and the Vi^ater itself is considerably 

 Baiter than the sea. That, however, is always the case 

 with freshwater lakes in their last dotage, as American 

 geologists have amply proved in the case of the Great Salt 

 Lake of Utah. Moving sand undoubtedly covers a large 

 space in both divisions of the desert, but according to Sir 

 Lambert Playfair, our best modern authority on the sub- 

 ject, it occupies not more than one-third part of the entire 

 Algerian Sahara. Elsewhere rock, clay, and muddy lake 

 are the prevailing features, interspersed with not infrequent 

 date-groves and villages, the product of artesian wells, or 

 excavated spaces, or river oases. Even Sahara, in short, 

 to give it its due, is not by any means so black as it's 

 painted. 



