CLIMATE. 15 



at the end of November the sky was overcast about half of the time, 

 and there were occasional gusts of cold, drizzling rain. 



Winds are probably more frequent and more violent in the Oued 

 Souf than in the other groups of oases mentioned. It would appear, 

 in fact, that windiness is the ordinary condition there. During the 

 winter, northwest and northeast winds prevail. From April to 

 October, however, the wind is generally from the south (the sirocco) 

 or the southeast (the simoom). The sirocco is the hottest wind, but 

 is less frequent than the simoom, which is generally more violent and 

 transports more sand. All these are winds that blow more or less 

 steadily for several hours and often days at a time. Cyclonic sand 

 storms also occur, arising suddenly and lasting but a short time. 

 Such storms are never accompanied by rain. 



Owing to the lack of natural vegetation (see PL II), and the fine- 

 ness of the sand with which the country is covered, strong winds 

 carry with them a great deal of material, so that the face of the land 

 is being constantly altered. This is shown by the fact that an 

 apparently fresh wagon track noticed by the writer on his journey 

 from Xefta was completely buried in many places by large heaps of 

 sand. During his four days' stay in the Souf country, a strong wind 

 blew constantly, often making travel difficult, as the particles of sand 

 stung the face and made it hard at times to keep the eyes open. The 

 air was frequently so full of sand that one could see but a few rods 

 ahead. 



The slopes of the dunes that border the gardens are very steep, so 

 that when a heavy wind is blowing much sand rolls down upon the 

 floor of the garden. Generally there is a fence or palisade along the 

 crest of the dunes, made by sticking palm leaves or pieces of gvpsum 

 rock close together (PL II, fig. 3; PL III, fig. 1; PL IV, fig. 1), but 

 this only partly arrests the blowing and drifting sand, and it is nec- 

 essary to remove it frequently from the gardens. The task is a labo- 

 rious one, as the sand must be carried up the steep hillside in baskets 

 and dumped on the outer sloj)e of the dunes. But if it were neglected, 

 in a few years the trees would be buried, especially in smaller gardens. 

 The writer saw several little gardens that had been abandoned by 

 their owners where the basin was almost filled and only the crowns 

 and a small part of the trunks of the trees still projected above the 

 soil. 



Another injurious effect of the sand-carrying winds is that when 

 harvested the dates always have more or less sand adhering to the 

 skin, and this must be brushed or washed oft' before they are fit for 

 export. Dates that had been kept for some weeks in the houses of 

 natives, and even those freshly gathered from the trees, were very 

 unpalatal)le to the writer on this account; although the Souafas them- 

 selves do not seem to mind eating a good deal of sand Avith their dates. 



