404 SCIENCE PROGRESS. 



Guettardi, N. Biarritzensis. Gasteropods and lamelli- 

 branchs are abundant, and sea-urchins of various kinds. 

 More than two-thirds of the species are said by Zittel to be 

 limited to the Libyan beds ; but there are sufficient which 

 are found elsewhere to determine the geological age with 

 some accuracy. The three nummulites mentioned occur in 

 the Lower Eocene of Europe and India. 



The upper division of the Libyan stage is typically 

 developed in the valley of the Nile between Siut and 

 Cairo ; and on the right bank opposite Minieh it is found 

 to consist of a succession of beds of limestone. It has also 

 been described by Fraas ( i i ) at one or two points between 

 Cairo and Suez. The most characteristic fossils are Alveo- 

 linas of various species (A. oblonga, A. frumentiformis, 

 etc.). Fabularia Zitteli is also abundant; and near Cairo 

 the rock is in places nearly filled with the claws of Callian- 

 assa, from which circumstance Fraas bestowed upon the 

 group the name of Callianassa bank. Nummulites are not 

 so common as in the lower division. 



An analysis of the fossils leads to the conclusion that the 

 upper division of the Libyan is to be correlated with the 

 Londinian (a part of the Lower Eocene), and Mayer-Eymar 

 finds the nearest analogue in the sands of Cuise-la-Mothe. 



The Mokattam stage occupies the greater part of the 

 Eocene plateau north of the Baharia oasis ; and near the 

 valley of the Nile a tongue of it extends upon the top of the 

 Libyan beds as far south as Siut. It also occurs over a 

 considerable part of the plateau east of the N ile. 



But it is in the hill of Mokattam near Cairo that it is 

 best known. Owing to its accessibility this locality has 

 been visited by many geologists, and several of them have 

 published the results of their visits in more or less detail. 

 The earliest satisfactory account is that of Fraas ; while in 

 more recent years we have descriptions by Zittel, Schwein- 

 furth (24), Mayer-Eymar (17), and others. Schweinfurth's 

 is by far the most complete and detailed account of the 

 stratigraphy of the hill, and is accompanied by a map and 

 sections in which he shows the distribution of the divisions 

 which he has recognised. Mayer-Eymar has proved the 



