THE DESERT OF SAHARA. 513 



sbeep, and goats, and retreat again to the coast lands as the sun gains power. At this 

 time of the year the wild animals — the lion, the gazelle, and the antelope — also wan- 

 der farther to the south, which at that time provides them, each according to its taste, 

 with the nourishment which the dry summer is unable to bestow ; while the ostrich, 

 who during the summer ranged farther to the north, then retreats to the south ; for hot 

 and sandy plains are the paradise in which this singular bird delights to roam. 



In the southern part of the Sahara the tropical rains, whose limits extend to 19° 

 north latitude, and in some parts still farther to the north, produce similar periodical 

 changes in the character of the desert. Under their influence the sandy plains are 

 soon covered with grasses and shrubs. In the dry season, on the contrary, the green 

 carpet disappears, and the country then changes into an arid waste, covered with stubbles 

 and tufts of mimosas. This beneficial change, however, does not take place every 

 year ; for the tropical rains frequently fail to appear on their northern boundaries, and 

 thus disappoint the hopes of the thirsty desert. 



S3 



