410 MARCHES THROUGH THE THIRST-LANDS. 



Africa significantly known as " Thirsts ") are often 

 considerable; even under the ordinary risks of the 

 desert carrying trade. The march in such cases has to 

 be continued almost without intermission, night and day, 

 until water has been reached the fatigues, therefore, 

 which are undergone by both men and animals, are 

 often extreme animals falling sick or exhausted must, 

 of course, inevitably be abandoned ; and human beings 

 must, under similar circumstances, be carried or walk 

 as best they can, until they recover or die. 



Fortunately throughout almost all extensive tracts of 

 desert the friendly oases form harbours of refuge, 

 which appear here and there, at certain well-known 

 points, like islands rising out of the ocean. Among 

 the ancients these spots were in fact known as " The 

 Islands of the Blessed." * 



Occasionally they are found singly: at other places 

 there are perhaps several which adjoin each other: 

 and sometimes a regular chain of them may be ob- 

 served, extending at intervals, for considerable distances 

 across the Desert Zone; an examination of a good map 

 of the Sahara, drawn on a large scale, such as that 

 published [by the French War Office of the Algerian 

 Sahara and the neighbouring territories, will make this 

 apparent, and shows the immense number of " Wadis " 

 or water courses which extend during the winter 

 rains from the mountains of the " Chaine Saharienne " 

 which lies to the southward of the Algerian " Tell, " 

 far into the Desert, until finally they are lost in the 

 sands. A great part of the Sahara consists of a deep 

 depression, now known to be considerably lower than 



* iiaxaQav vfjsol, see Murray's Handbook for Egyft, 8th Edit., 

 p. 17. Also Herodotus, Book iii (Thalia), cap. 26. 



