,428 Scientific Intelligence. — Geology. 



others. If we had been restrained by the remark, so often re- 

 peated, that the Mediterranean is too confined to allow tides to 

 be observed, we should not now have known that they are quite 

 sensible in the Achiatic ; and we should have been ignorant that 

 at Chioggia and Venice they rise more than a yard. — Arago. 



GEOLOGY. 



12. Geology of the Zahara Desert. — From M. Elie de Bemi- 

 mon^s Instructions to the Scientific Commission to Algiers. — M. 

 Rozet, from the observations he has himself made upon the ter- 

 tiary strata in the neighbourhood of Algiers and Medeya,and ac- 

 cording to the information he has received from the celebrated 

 traveller M, Rene Caillie, thinks it highly probable that the 

 tertiary formation of the district of Algiers constitutes the soil 

 of the Great Desert of Zahara. He considers that sandstones 

 and the tertiary limestones will be met there in horizontal beds, 

 covered with great masses of sands, which will be found to be 

 nothing more than those which very frequently appear at the 

 upper part of the sub-Atlantic tertiary formation,* with this 

 difference, that to the south of the Great Atlas the sands will 

 have acquired an exceedingly great development. The argil- 

 laceous marls, which, according to M. Rozet, must exist at the 

 lower part of the tertiary series in the Zahara Desert, as well 

 as near the Atlas, as they readily retain water, make it highly 

 probable that abundant springs would appear upon boring. 

 Draw-wells might thus be easily established. Mr Shaw even 

 mentions, that in the villages of Wad-reag they are in the habit 

 of procuring water by machinery, which reminds us of our 

 Artesian wells, or spouting fountains. This fact is alluded to 

 by M, Arago in his able article upon Les Puits Artesiens in 

 the Annuaire for 1834f This possibility of establishing spout- 

 ing-fountains, not only in the Zahara Desert, but also in many 

 places throughout the Algerine district, not excepting many 

 near the coast, is so important, that it deserves to be particu- 

 larly recommended to the attention of those who superintend 

 the geological department of the commission. Again, the sands 

 of the Desert of Zahara, and of those much smaller deserts 



* Rozet names the Tertiary deposits of Algiers sub- Atlantic, 

 t A translation of this Memoir is published in vol. xviii. of Edinburgh 

 New Philosophical Journal. 



