— 21 
as 40°, 45 and 47° Centigrade; or 104°, 113°, 116°, Farenheit. The 
minimum thermometers as 5*5°, — 0*7°, 4 # 0° Centigrade; or 42°, 31°, 
39° Farenheit. The rainfall at Alexandria, Cairo and Assuan respectively 
may be taken as 235, 31, and 0 millimetres; or 9, 1 J, and 0 inches. 
The heavest rainfall in any individual year at Alexandria and Cairo 
respectively has been 308 and 55 millimetres; or 12 and 2 filches. The 
lightest rainfall at Alexandria and Cairo respectively in any individual 
year has been 108 and 7 millimetres; or 4 J and J inches. Assuan is 
practically rainless. It does rain sometimes at Assuan, but there has 
been no rain during the last three years while meterological observations 
have been taken. 
7. The Geology of the Nile Valley. — South of Gondokoro along 
the Victoria and Albert Niles, and at the lakes, the rocks are generally 
granites, crystalline schists and quartzites. The hills of Uganda are 
covered with red clay and marl on the higher lands, while the valleys 
consist of a rich black loam. All the cataracts are granites and 
granitic rocks or diorites. The Ruenzori range consists of lofty 
volcanoes. The surface of the ground is covered with a fine Kankar 
(nodulated limestone) in many places. North of Gondokoro the plains 
are formed of sandy deposits mixed with coarse peat in places. The 
hills of the Bahr-el-Gazelle and Arab river are all crystalline. Abys- 
sinia is a volcanic plateau. It is the detritus of this rich volcanic soil 
swept down by the Blue Nile and Atbara which constitutes the richness 
of the soil of Egypt and of the water of the Nile. Those parts of the 
eastern Sudan south of Khartoum and El-Damer and at Kassala, which 
are the deltas of the Blue Nile, the Binder, the Rahad, the Atbara, 
and the Gaash, are possessed of a soil in every sense similar to that of 
Egypt itself. At Khartoum and in the bed of the Blue Nile at Kamlin 
are extensive deposits of nodular limestone corresponding to the Kan- 
kars of India. 
The main Nile from Khartoum to Assuan flows between low hills 
and tables of Nubian sandstone overlying crystalline rocks of gneiss, 
mica schists, hornblendic granite and red granite. Where the crystalline 
rocks come to the surface we have cataracts ; where the Nubian sandstone 
is at the surface we have reaches of unbroken water. 
From Assuan (*) to near Edfu the Nile flows between hills of Nubian 
sandstone, the best known of which is Gebel Silsila. From Edfu to 
0) Condensed from a description of the geology of the Nile Valley in Egypt written by 
Capt. Lyons for the second edition of “Egyptian Irrigation”. 
