BOOK II. 



THE DESERTS OF SAXD:THE DESERTS OF EUROPE AND AFRICA. 



CHAPTER I. 



THE RAINLESS DESERT THE BED OF A SEA THE DEAD SEA. 



Sandy Deserts may with equal, nay, with greater 

 accuracy, be entitled Salt Deserts, Rainless Deserts, Seas 

 of Sand ; for they present at one and the same time all 

 these characters, and the three last, though less generally known than 

 the first, are the most essential. 



The soil is generally covered with a thick stratum of sand ; but 

 in several places it also exhibits great walls of rock, and in others 

 masses of rolled or shattered pebbles. The subsoil is nearly always 

 of a gypseous or calcareous nature, rarely clayey ; wherever it is 

 porous and permeable, it is impregnated with salt, which rises to the 

 surface, or is held in solution in the subterranean basins of water, the 

 thermal springs, the ponds, and the lakes. The saline efflorescences 

 of the deserts of Persia and Oriental Asia not only suffice for the 

 wants of the inhabitants, but supply the great Asiatic caravans with 

 their principal article of exportation. 



The atmosphere of the Deserts is not less dry than their sands 

 and rocks. The sky wears a perennial azure, more or less veiled in 

 haze, or rather spotted with a few clouds. Johnstone represents 

 them, in his admirable " Physical Atlas," by two white unequal 



