276 SIB WILLIAM DAWSON, C.M.G., LL.D., F.E.S., 



nearly horizontal position of their layers, from their con- 

 taining silieified wood so distributed, and with its cracks 

 filled by sandstone, &c, as to show that it was embedded in 

 the natural state, and afterwards silieified, and by the 

 irregular pipes or craters passing through the hardest parts 

 of the beds, and apparently the channels of geysers, or 

 fountains of heated water. The date of these aqueous 

 outflows must have been little later than that of the 

 beds of sand, and while they were still unconsolidated, 

 and their drift wood in a recent state. Direct volcanic 

 action is not known in connection with Jebel Ahmar, but 

 volcanic masses of Tertiary age exist near Abu Zabel, 

 between Cairo and Ismailia, and also in the Nubian Desert, 

 which may be of the same age. These have been described 

 by Beyrich, Schweinfurth, and Arzruni, and by Zittel.* 

 They afford the basalt mentioned in previous pages. 



The Miocene or "Tongrien" sandstone of Jebel Ahmar 

 may be estimated at 400 feet in thickness. It consists of 

 siliceous sand partially rounded like the desert sand, but with 

 many angular grains, and with the interstices more or less 

 filled in with hyaline silica, sometimes entirely consolidating 

 the mass. In some of the beds are layers of pebbles of 

 quartz, agate, and jasper, many of which are evidently 

 derived from the siliceous concretions in the underlying 

 Eocene limestones. The colours vary from pure white to 

 light red and dull purple, and the rock is often beautifully 

 striped and mottled. From the enormous mass of chips 

 around the hill, and the deep excavations in its sides, these 

 beds of sandstone would seem to have been quarried from 

 the earliest times, and they still furnish materials for mill- 

 stones and for macadamising the streets of Cairo. 



The harder varieties must have afforded the earliest 

 colonists a desirable material for hoes, diggers, hatchets, and 

 war- clubs, and tbeir successors continued to use it largely 

 for hammers and polishers and pestles, as well as for mortars 

 and millstones. But from the earliest periods of Egyptian 

 sculpture and architecture, the beauty and durability of this 

 rock were recognised, and the perfecting of the art of drilling 

 hard stones in the palmy days of ancient Egypt enabled this 

 refractory material to be employed even for the formation of 

 monolithic shrines and colossal statues. 



Of the former, a shrine taken from the temple of Pithom, 



* Proceedings of Royal Academy, Berlin, 1882. 



