3 8o SCIENCE PROGRESS. 



of the Palaeozoic rocks runs along the escarpment of the 

 oreat Hamada el Homra. At Bir el Hassi Overweo; found 

 that the Cretaceous beds of the top of the Hamada rest 

 upon sandstone and marl, in which he discovered the 

 Devonian fossils Spirifer Bouchardi, Terebratula \Rhyn- 

 c hone Ha] Daleidensis, T. [7?.] longinqua (17). 



Continuing the line between the Palaeozoic and Cre- 

 taceous along the escarpment of the Hamada, we find that 

 it leads us to the Libyan Desert, where nothing is known of 

 the rocks until we reach the oasis of Kufra. 



Throughout the whole of the area from the Cretaceous 

 escarpment southwards to the gneissic series, the Palaeozoic 

 beds are nearly horizontal, and they consist for the most 

 part of sandstone resting upon marl or marly slate. This 

 is well seen in the Akakus range, east of Ghat, of which a 

 sketch is given by Barth. Fossils have been found in the 

 sandstone and marl at several places besides those already 

 noticed. In the Tasili plateau Roche discovered a 

 trilobite allied to Proetus Cuvieri, a tail of Calymene (?), 

 Strophomena quadrangularis, Atrypa prisca, A. reticularis, 

 Ortkis, Spirifer, and Rhynchonella ; and he concludes that 

 these beds are of Devonian age (13). At the northern end 

 of the Akakus range Duveyrier found fossils which were 

 referred by De Verneuil to Spirifer (near to Sp. ostiolatus 

 and Sp. siibcuspidatus), and Chonetes crenulata. Here 

 again a Devonian age is indicated (30, p. 62). 



East of the Libyan Desert, which causes a serious break 

 in the continuity of our map, it is the so-called Nubian 

 sandstone which rests upon the crystalline rocks. It 

 occupies a large space between the Cretaceous of the 

 Dakhla Oasis and the Archaean rocks of Upper Egypt, and 

 it is found also in the Oasis of Kufra (32, p. 330). The 

 geological position of this sandstone has been much dis- 

 cussed, for till recently no fossils had been found in it 

 except silicified wood. From the fact that the Upper 

 Cretaceous of the Libyan Desert is quite conformable upon 

 it, Zittel concluded that it must probably be of Lower 

 Cretaceous age. But the discovery of Carboniferous 



