ALKALI CONDITIONS AT OURLANA. 



89 



at the side of a drainage ditch. The surface crust obtained here shows the following 

 composition, as analyzed by Mr. Seidell, by extracting with an excess of water 20 times 

 the weight of the sample: 



TABLE 23. Per cent of alkali soluble in excess of water, in surface crust from Mrdier, 



Algeria. l 



r. Seidell's original analysis of the sample from this station is as follows: 



This crust is remarkable among those collected in the Sahara for its low content of 

 calcium sulphate (8.277 per cent of total alkali) and the high content of magnesium 

 sulphate (21.86 per cent of total alkali). The extreme sterility of the sink where the 

 sample was secured may be due in part to the excess of magnesium over lime, which 

 has been shown by Loew a to be very injurious to most plants. This was the only 

 sample obtained in the Sahara, where magnesium sulphate was in excess of gypsum. 

 Common salt makes up one-half (52 per cent) of the crust. 



ALKALI CONDITIONS IN RELATION TO DATE CULTURE AT OURLANA, ALGERIA. 



Going southward from M'rai'er one soon enters the Oued Rirh region proper. The 

 Oued Rirh or Rirh River is a chain of chotts (salt lagoons or dry salt beds) occupy- 

 ing a partially filled up, dry valley, which runs from Tougourt almost due north to 

 the Chott Melrirh, with a gradual fall to the north, amounting to some 270 feet in the 

 70 miles from Bledet Amar & to Chott Merouan (see map, PI. II, p. 76) . The Oued 

 Rirh has a very shallow valley, bordered on the west by a nearly flat plain of sandy 

 loam soil (largely planted to date palms), which rises gradually toward the barren 

 hills, which are reached at a distance of from one-half to 10 miles from the valley. 

 To the east of the chain of Chotts this country is sandy, and dunes occupy most of 

 the surface. Small dunes sometimes occur on the west side of the valley. 



This valley is some 200 feet above sea level at Tougourt and is slightly below sea 

 level where it enters the Chott Merouan. It is abundantly supplied with flowing 

 artesian wells and is one of the most celebrated date regions in the world. The 

 famous Deglet Noor date, reported in Tunis to have originated in the oasis of Bledet 

 Amar near Temacin at the southern end of the Oued Rirh, is largely grown here and 

 constitutes almost the sole export. In all parts of the Oued Rirh date culture is the 

 chief industry, and in many oases the date is the only plant grown, as the very 



Loew, O. Relation of Lime and Magnesia to Plant Growth, Bui. No. 1, Bureau 

 of Plant Industry, U. S. Dept. of Agriculture, and also Kearney and Cameron, Report 

 71, U. S. Dept. of Agriculture. 



& Marked Bled et Ahmar in the map, Plate II, page 76. 



