66 René Fourtau—The Eocene of Egypt. 
This demarcation line also corresponds with a notable change of 
facies and with the appearance in Egypt of the large Nummulites 
constituting the JV. gizehensis group. ‘These two divisions have been 
long established and adopted almost unanimously by geologists who 
have studied the Kocene of Egypt. They are the Libyan and 
Mogattamian Stages. 
The Libyan Stage can be subdivided into— 
1. Lower Libyan, where C. Delanouwec is present alone with 
Linthia cavernosa. 
2. Middle Libyan, in which with C. Delanowei and L. cavernosa 
appear Plestospatangus Cotteaui and the group of Megapneustes, which 
is only found at this horizon. 
3. Upper Libyan, long ago separated under the name of ‘‘Alveolina 
Series’’, which still contains some C. Delanouet, but none of the other 
species. These are replaced by small forms, of which the most 
abundant is Hypsospatangus Lefebvrer. 
The Mogattam Stage, which following the rules of nomenclature 
we should term Moqattamian, can be easily divided into two sub- 
stages— 
4. The Lower Moqattamian is characterized by large conoclypeiform 
Echinolampas, together with Schizaster africanus and Huspatangus 
Sormosus. 
5. The Upper Moqattamian in which the sea-urchin species of large 
size are replaced by others that are quite small, such as Thagastea 
Lucian, Echinolampas Cramert, Anisaster gibberulus, accompanied by 
Schizaster vicinalis, Agassiz, while in the uppermost layers the genus 
Clypeaster appears for the first time in Egypt. 
The synchronization of the local divisions is somewhat delicate, 
and has of late given rise to somewhat lively discussion. The 
Echinids have not been used to establish the divisions adopted in 
Europe, and latterly efforts have been mainly applied to determining 
a Nummulite scale, which, it must be admitted, has given good 
results in many places, but which might give rise to criticism when 
applied to other localities and especially North Africa. It is not 
easily to be explained, for instance, why, in Tunis and Algeria, the 
beds with Mummutlites. gizehensis are attributed by everybody to the 
Lower Eocene, whereas in Egypt all agree as placing them in 
the Middle Eocene. The study of the Cercthium group has given 
fairly good results in the Paris Basin, but division on such a basis 
is impossible in Egypt, where these Gasteropods are rare, and when 
present are usually distinct species. 
It might be therefore useful to take the succession of echinid 
faunas and changes of facies as our basis in attempting to subdivide 
the Eocene of Egypt, and to attach only a relative value to 
synchronizations founded on widely separated faunas. The Table 
(p. 67) indicates the solution which appears to me the most 
satisfactory. 
The synchronizations which I propose in this Table appear to me 
rational. There might, however, be discussion as to the desirability 
