1865.] Geology and Palaeontology. 675 



of its heat, but would also become charged with moisture, which being 

 deposited on the mountains in the form of snow, would add to the 

 volume of their glaciers ; that is to say, the glaciers would be larger, 

 positively by the sirocco bringing material that it does not bring now, 

 and negatively by its not melting the snow and ice, which it does now 

 to a considerable extent. It therefore appears that the Sahara is very 

 intimately connected with the present moderate climate of Europe. 



Another phenomenon is the one which has been discussed in this 

 Journal, namely, What influence has the Sahara on the north-east 

 trade- wind '? The cause of this wind has generally been stated to be 

 a rush of cold air from the north, the direction of which is modified 

 by the rotation of the earth on its axis. The existence of a south- 

 east trade-wind on the other side of the equator is a strong argument 

 in favour of this explanation, and against the view that the sister 

 wind is due to a local cause ; but that the Sahara may modify 

 the force and direction of the north-east trade does not appear 

 improbable. 



The Sahara was submerged, then, during the Glacial Period ; but 

 what was its condition previously ? This is the question that has 

 chiefly induced us to notice the phenomena connected with the great 

 African desert in this Chronicle, as the answer to it is of great im- 

 portance to those who take an interest in Tertiary geology, and has 

 only just been published. 



The artesian wells sunk by the French have proved the existence 

 of underground sheets of water at depths ranging to as much as 500 

 feet, and it is in boring them that so many facts bearing on the 

 History of the Sahara have been discovered. M. Ville has written 

 several memoirs descriptive of different portions of the desert, and 

 his last production, entitled " Notes d'un Voyage d'Exploration dans 

 les Bassins du Hodna et du Sahara," and published simultaneously in 

 the last number of the ' Annales des Mines,'* and in the ' Bulletin 

 de la Societe Geologique de France,'! is remarkably important and 

 contains a host of most interesting facts bearing on the distribution 

 of these underground sheets of water. The point to which we now 

 wish to draw attention is this : M. Ville shows that the surface in one 

 part of the desert is formed of a Quaternary formation (Post-pliocene), 

 to which he gives the name " Terrain Saharien," and nearer the 

 mountains of an underlying series of deposits of Pliocene age, con- 

 taining in some places marine fossils, namely, Leda subnicobarica, 

 Pinna cristellaria, Cassis, Tomatella, &c. So far as we know, this 

 fact is quite new, at least to geologists in England, and we await with 

 much curiosity and impatience the publication of complete lists of 

 the fossils, for it is more than probable that the Miocene fauna of the 

 south of Europe, Madeira, &c, may have journeyed eastwards through 

 the ancient desert-sea, and if this has been the case we may expect to 

 find some traces of their passage in these Pliocene deposits of the 

 Sahara. That the beds in question are really Pliocene appears certain, 

 as their age is given on the authority of M. Deshayes. 



* 6 me eerie, vol. vii., 2 me livr., pp. 117-156. t 2 mc seiic, vol. xxii. 



