314 PROFESSOR E. HULL, LL.D., F.R.S., F.G.S., ON THE 
above the Mediterranean; and, the distance between Assouan 
and Cairo by the river being 556.miles, the average fall is 
little more than half a foot in a mile. Between Phile and 
below Assouan the river passes through a labyrinth of grani- 
tic and crystalline rocks, causing a series of rapids, known as 
the First Cataract. The Arabian hills, forming the right 
bank of the river, break off in a line of cliffs throughout 
nearly their whole length. In the neighbourhood of Assouan, 
they rise little more than 200 feet above the river, but they 
go on increasing in height to the vicinity of Thebes, where 
they attain an elevation of 1,065 feet above the Nile; and 
from this northwards, they have a gradual fall, but rise again 
on approaching the apex of the Delta to about 900 feet. 
Above Cairo, the cliffs of Eocene limestone are worn into 
terraces and caverns, indicating former depressions of the 
whole land surface beneath the sea, and ancient sea margins 
to which [ will have occasion to refer again. Below Assouan, 
the granitic rocks are covered by the Nubian sandstone, which 
extends along both sides of the river as far as Esneh, about 
85 miles below Assouan, where it in turn passes below white 
limestone strata, referable to the period of the Cretaceous 
Limestone or Chalk of England.* 
Part IV.—GEOLOGICAL FORMATIONS. 
Such being the general form and features of the region now 
under description, it remains to give very briefly some 
account of the geological formations of which it is built up; 
and, as this subject has already been so fully dealt with by 
ceologists of eminence, only a slight sketch will be necessary 
here before we come to discuss the physical changes which 
the region has undergone from the time when the land first 
emerged from below the ocean until it assumed its present 
form and condition. 
(1.) Fundamental Crystalline Rocks—The rocks which 
constitute the foundation of all others in this part of the 
world are probably of the age known as “ Archean” or 
“Laurentian.” They form the ridge which crosses the Nile 
at the First Cataractt and extend into the protaxial range of 
* An excellent account of the physical phenomena connected with the 
Nile and its channel is given by Mr. Horner in his paper on Lower Egypt, 
Philosophical Transactions, 1855; also in Réclu’s Nouvelle Geographie, 
vol. x. Space does not permit of any fuller description here. 
+ These rocks have been described by Lieut. Newbold, F.R.S., Quart. 
Jour. Geol. Soc., vol. iv, p. 324; J. C. Hawkshaw, zbid., vol. xxiii, p. 115 
