104 REPORT — 1860. 



out any springs of fresh water, yet affording at intervals throughout its whole extent 

 a never-failing supply of sweet water, through artesian wells penetrating the upper 

 limestone. An immense population is supported by this Wed It'iiir, which is for many 

 days' journey one continuous line of oases, such as El Marier, Tameina, Tuggurt, 

 Temacin, and after a further interval, in which its traces are lost, it reappears in the 

 oases of N'Goussa and Waregla, and gradually is lost in the highlands of the south. 

 But it is probable that even here the subterranean course of the water can be traced, 

 and that the Touareg owe their means of subsistence to their knowledge of wells on 

 this line. 



The Wed R'hir terminates in the Chott Melr'hir, a depression probahly eighty feet 

 below the Mediterranean sea-level and the lowest point of the whole Sahara. This 

 basin extends eastwards to the Chott el Melah (LakeTritonis), at a greater elevation, 

 but yet scarcely rising to the sea-level, from which it is separated by some thirty miles 

 of sand-hills and rocks. 



Proceeding northwards of the Melr'hir, we rapidly lose all traces of the diluvial 

 deposits, and come upon the chalk, chalk-marl, and greensand in regular succession, 

 dipping generally southwards. The three southernmost ridges of the Mons Aures, 

 viz. the Djebel Checha, the Dj. Khaddou, and Dj. Amar, present us with these three 

 stages of the cretaceous group in order. 



When we advance to the north of Biskra, the boundary between the Tell and the 

 eastern Sahara, the mountains are composed of masses of nummulite limestone, with 

 bands of gypsum and occasional interruptions of rock-salt, mixed with layers of marl. 

 One of these mountains of rock-salt has been described long since by Dr. Shaw — that 

 of El Outaia. 



There are many salt deposits, sometimes masses of isolated rock-salt, perfectly pure, 

 of many hundred yards in circumference, as at Hadjera el Mehl (or Kochers de Sel), 

 more frequently in the form of layers or incrustations on the plains near the Chotts, 

 or beds of evaporated lakes. Some of the isolated rock-salt hills have been suggested 

 to have been eruptions of argillaceous mud, gypsum, and rock-salt across the secondary 

 and tertiary deposits. 



In such a country as the Sahara, we cannot expect to find much mineral wealth, 

 beyond the salt, gypsum, and natron. There is a quarry of oxide of manganese in the 

 Djebel Trisgrarine, traces of lignite and carbonized trees at Ain el Ibel, and many hot 

 springs — some pure, others strongly impregnated with chlorine. The temperature of 

 one of these I found to be 125° Fahr., of others from 75° to 95° Fahr. In one of the 

 latter were swarms of a little fish, Cyprinodon dispar, also found in the warm springs 

 of Egypt. 



On the Invertebrate Fauna of the Lower Oolites of Oxfordshire. By J. F. 

 Whiteaves, F.G.S., Honorary Member of the Ashmolean Society, Oxford. 



Although the physical geology of the neighbourhood of Oxford is, with some ex- 

 ceptions, tolerably well understood, our knowledge of its palieontology, especially of 

 the invertebrate division of the animal kingdom, is very meagre and unsatisfactory. 

 The only exception I am aware of is a detailed list of the fossils of the Stonesfield 

 Slate, in a paper contributed by Prof. Phillips to the volume of " Oxford Essays" for 

 ]855, entitled " The Neighbourhood of Oxford and its Geology." 



The following brief sketch of the Invertebrate obtained from the Great Oolite, 

 Forest Marble, and Cornbrash during several years' collecting, must be considered as 

 temporary only, nearly every day spent in practical investigation revealing fresh 

 species, only a very small area having been carefully explored, and even that small 

 area by no means so thoroughly as one could wish, Hence the few inductions that 

 I have, as it seems to me, legitimately deduced from facts, must be considered as 

 approximate results only in the present state of our knowledge. To Prof. Phillips's 

 list of the fossils of the Stonesfield Slate, I am enabled to add twenty-eight species of 

 Mollusca ; these are, — 



Ammonites Waterhousci, Mor. and Lye. Nerita hemisphanica, Roemer. 



Cerithium ? minuta, Sou-. 



Natica canaliculata ?, Mor. and Lye. costulata, Deshaues. 



Eulima communis, Mor. and Lye. (castsonly. rugosa, Mor. and Lye. 



