346 RAINLESS DISTRICTS. 



days, as the existence of considerable numbers of dry 

 water courses, dry saline lake beds, and the marks of 

 ancient torrents, conclusively proves; whilst during 

 other years the rains may be practically nil indeed, in 

 most of the principal deserts, according to the reports of 

 residents inhabiting the various oases, it is stated that 

 sometimes for several years in succession, not a drop 

 of rain has been known to fall. Thus in the oasis of 

 " Tuat " in Southern Morocco it is said " to rain scarcely 

 once in twenty years." * Some of the Arabs inhabiting 

 this region have even been known to doubt the fact 

 of its being possible for water to fall from the sky. 



The phenomenon of the tropical rains has already 

 been discussed in considerable detail; the incessant 

 rains of the equatorial zone being shown to become 

 changed, first, into zones of double rainy seasons; and 

 next, into those where a single rainy season prevails; 

 this latter gradually getting shorter and shorter, until 

 at length there is no longer any regular rainfall; the 

 rains become more and more intermittent, and we enter 

 the almost rainless desert zone. 



Endeavours have from time to time been made by 

 various observers to try and fix the exact points where 

 these changes may be said to take place ; but they are 

 so gradual in their nature, and so liable to be modified 

 by local circumstances, that the attempt has been 

 attended with only very partial success, for these 

 countries are visited by comparatively few travellers, 

 and they generally endeavour to time their journeys so as 

 to pass through at a period when native reports show 

 that the wells are fairly well supplied; the caravan 



* Stanford's Compendittm of Geography and Travel for Africa, 

 2nd Edition of 1880. Edited by Keith Johnston, p. 26. 



