318 PROFESSOR E. HULL, LL.D., F.R.S., F.G.S., ON THE 
abundant. Thus we can understand how that, with but little 
discordance of stratification, the specific forms became 
changed. 
The Nummulite limestone is fairly laid open to view in the 
quarries of Gebel Mokattam, near Cairo, and amongst other 
forms may be seen well preserved specimens of crabs, with 
their limbs attached to the crustaceous body; also large 
Nautili, and Echini of the genera Echinolampas and Spatangus. 
The ancient quarries on the night bank of the Nile above 
Cairo are those which yielded the stone of which the two 
great Pyramids have been constructed.* 
The combined thickness of the two limestone formations, 
the Cretaceous and Eocene, in the Egyptian territory may, 
according to Zittel, he estimated at nearly 4,000 feet ; and as 
these strata were formed mainly from the remains of marine 
animal forms such as Foraminifera, Crinoids, Crustaceans, and 
Molluscs, the length of time included in this period of ac- 
cumulation of material is necessarily very vast indeed, 
(4.) Miocene Stratz.—It is probable that at the close of the 
Eocene stage, the bed of the ocean was again subjected to 
elevatory movement, some portions became dry land, others 
were converted into inland lakes or estuaries. In these 
latter, clays and sandstones were deposited, and the plants 
peculiar to Africa grew round their margins, or partially were 
aquatic. The stems of these trees have in several places 
become silicified, and afford at the present day the remark- 
able spectacle of the silicified forests of Jebel Ahmar, near 
Cairo, and of the Libyan Desert, in lat. 30° N. and long. 
29° 30' E., called by Zittel “the Nicolien Wald,” from the 
prevalence of the trees called MNicolia Aigyptiaca and N. 
Oweni, to which may be added several other forms, includ- 
ing a conifer and a palm. The presence of those trees ina 
region now arid and treeless shows that the climate of this 
region has undergore a great change in Post-tertiary times: 
to this subject I shall again refer.f 
The Miocene period in Egypt, as in Europe and the 
British Isles. was one remarkable for terrestrial movement 
* It is lamentable to reflect that the Mahomedan Caliphs in their zeal 
for the religion they had adopted showed little respect for the memory of 
the ancient Lords of Egypt, and did not scruple to strip the polished and 
sculptured casing of marble from off the pyramids in order to obtain 
material for building their mosques, and the walls of the city. 
+ Zittel, loc. cit., p. exxxiii. The leaf of an oak, Quercus ilex, was found 
by this author in the Oasis of Chargeh. 
