1 



18 AGRICULTURAL EXPLORATIONS IN ALGERIA. 



often collected into dunes of g-reater or less size (erg). There arc 

 also extensive areas where the nearly- plane surface is composed of 

 smooth rock or hardened alluvial clay (hamada). 



A great valley, some 60 miles long and about 12 miles wide, known 

 as the "Oued Rirh,'' forms the most valuable portion of the Sahara of 

 Algeria. It is realh' the bed of an extinct river. It is largeh' below 

 or only slightly above sea level, the maximum depression — the exten- 

 sive salt lake known as "Chott Melrirh'' — being 1(>7 feet below sea 

 level. Subterranean streams of considerable volume underlie the 

 surface in this region. These are doubtless fed b}' water which flows 

 down from the mountains and sinks through the desert sands until it 

 meets an impermeal)le layer of clay or of rock, over which it flows. 

 The Oued Rirh Vallev has been described as a ''small Egypt with a 

 subterranean Nile." B}^ means of w'ells this water has been utilised ^ 

 in the creation of oases, where hundreds of thousands of date palms 

 flourish. M 



The idea, once generalh' held, that the entire Sahara is the bed of " 

 an ancient sea has been abandoned. Only for the part known as the 

 Oued Rirh, a small fraction of the whole desert, is this theory still 

 entertained by some authorities. Here there is a series of large salt 

 lakes, some of them below the level of the sea, which extends across 

 Tunis almost to the Gulf of Gabes. 



CLIMATE. 



The greater part of Algeria has a warm, temperate climate, very 

 similar to that of California. The climates of both countries are 

 determined in large measure bv the combined influence of three fac- 

 tors — the ocean, the mountains, and the desert. In Algeria, as in i 

 California, most of the rainfall occurs during the mild winter, while 

 the long summer is almost perfectly dr}'. Furthermore, the direction 

 of the prevailing winds at different seasons is in both countries largelv j 

 efl'ective in regulating conditions of temperature and of rainfall. The " 

 lower part of the coast region has a wet and a dry rathei' than a warm 

 and a cold season. The higher mountains, however, and the high 

 plateau are characterized bv a decidedl}- cold winter. Algeria would 

 be wholly a desert were it not for the northwest winds, charged with 

 humidity, which blow from the sea, especially during the winter and 

 spring. Their influence is, of course, most marked in the coast 

 region, which has, in consequence, the heaviest rainfall, the most 

 humid atmosphere, and the most luxuriant vegetation of any of the 

 three zones. 



The mountain chains which follow the coast line intercept a large 

 part of the moisture carried by the sea winds, so that, while their 

 northern, seaward slope has a comparativelv heavy rainfall, their 



