60 STEPPES AND DESERTS. 



parts of the earth. In the limestone formations of the 

 "white Harudsh" (Harudje el-Abiad), which perhaps 

 belong to the old chalk, Hornemann found an immense 

 number of fossil heads of fish. Ritchie and Lyon remarked 

 that the basalt of the Soudah mountains, like that of the 

 Monte Berico, was in many places intimately mixed with 

 carbonate of lime, a phenomenon probably connected with 

 eruption through limestone strata. Lyon's map even mentions 

 dolomite in the neighbourhood. Modern mineralogists have 

 found syenite and greenstone in Egypt, but not basalt. 

 Possibly the material of some of the ancient Egyptian vases, 

 which are occasionally found of true basalt, may have been 

 taken from these western mountains. May " Obsidius lapis" 

 also have been found there ? or are basalt and obsidian to be 

 sought for near the Red Sea ? The strip of volcanic or 

 eruptive formations of the Harudsh, on the margin of the 

 African desert, reminds the geologist of the augitic vesicular 

 amygdaloid, phonolite, and greenstone porpyhry, which are 

 only found at the northern and western boundaries of the 

 Steppes of Venezuela and of the plains of the Arkansas, 

 as it were on the hills of the ancient coast line. (Humboldt, 

 Relation Historique, torn. ii. p. 142 ; Long's Expedition to 

 the Rocky Mountains, vol. ii. pp. 91 and 405.) 



( 7 ) p. 3. " When suddenly deserted by the east wind 

 of the tropics in a sea covered with weed" 



It is a remarkable phenomenon, well known among 

 sailors, that in the vicinity of the African coast (between 

 the Canaries and the Cape de Verde Islands, and particu- 

 larly between Cape Bojador and the mouth of the Senegal), 



