Scientific Intelligence. — Geology, 4^ 



which lie between the mountains of Algiers, should be exa- 

 mined, with an especial relation to the sands of downs ; so that 

 the differences which exist between these two varieties of sands 

 may be ascertained, both as it regards their present circum- 

 stances and their respective origins. It has long been known that 

 the sands of the deserts near Egypt contain trunks of silicified 

 trees. Some indications would lead to the supposition, that 

 these may also be found in the deserts of Algiers ; and it would 

 be interesting to come to a definite conclusion on this point, as 

 the presence of such silicified trees would tend to establish the 

 tertiary origin of the sands. A great sandy desert, viz. that of 

 Anga, separates, on the east, the regency of Algiers from the 

 kingdom of Fez. This desert is undoubtedly analogous in its 

 geological origin to the Great Desert of Zahara, and it would 

 be of much easier access to the members of the scientific expe. 

 dition than the other. One of the most curious-facts which the 

 deserts of Africa and Asia present is, that their soil is frequently 

 salt. Chloride of sodium is spread over the soil of Barbary in 

 surprising abundance. According to M. Desfontaines, the 

 ground, throughout nearly the whole extent of the regency of 

 Tunis, is impregnated with so great a quantity of sea-salt, that 

 the majority of the springs are salt-springs. It is by no means 

 rare to observe, when the summer heat has evaporated the 

 stagnant waters of low places, that a considerable extent of the 

 surface is encrusted with the salt which had been dissolved and 

 accumulated by the winter's rains. These plains are usually 

 denominated Sibkah, in other words, salted earth. In winter 

 they are usually covered with water, and then appear like so 

 many great lakes ; but when dried in summer, they very much 

 resemble great bowling-greens covered with beautiful turf. 

 Some of these Sibkahs have a hard and solid bottom, without 

 any mixture of earth or gravel, which retains the salt, and forms 

 a crystalline crust after the rains. Saline deposits of this sort 

 occur near Arzew, and in several other localities. It would be 

 interesting to examine the relations which exist between the 

 salt that is thus superficially spread over the surface, and the 

 masses of rock-salt which also exist in the district of Algiers. 

 Shaw considers them nearly allied, for he remarks that the 

 salt of the Lake Marques, which is also called Bahirah-Pha* 



VOL. XXV. NO. L. OCTOBER 1838. F f 



