Appendix II. 
Phytogeography and Geology. 
“Koypt is the gift of the Nile” 
Herodotus. 
The Nile, which created the valley home of the early Egyptians, 
rises three degrees south of the equator, and flowing into the Mediter- 
ranean at over thirty one and a half degrees north latitude, it attains 
a length of some four thousand miles, and vies with the greatest 
rivers of the world in length, if not in volume. In its upper course 
the river, emerging from the lakes of equatorial Africa, is known 
as the White Nile. Just south of north latitude sixteen at Khartum, 
about thirteen hundred and fifty miles from the sea, it receives from 
the east an affluent known as the Blue Nile, which is a considerable 
mountain torrent, rising in the lofty highlands of Abyssinia. One 
hundred and forty miles below the union of the two Niles the 
stream is joined by its only other tributary, the Atbara, which is a 
freshet not unlike the Blue Nile. It is at Khartum, or just below 
it, that the river enters the table land of Nubian sandstone, under- 
lying the Great Sahara. Here it winds on its tortuous course bet- 
ween the desert hills, where it returns upon itself, often flowing due 
south, until after it has finally pushed through to the north, its 
course describes a vast S. 
In six different places throughout this region the current has 
hitherto failed to erode a perfect channel through the stubborn 
stone, and these extended interruptions, where the rocks are piled 
in scattered and irregular masses in the stream, are known as the 
cataracts of the Nile. These rocks interfere with navigation most 
seriously in the region of the first, second and fourth cataracts; 
otherwise the river is navigable almost throughout its entire course. 
At Elephantine it passes the granite barrier which there thrusts up 
its rough shoulder, forming the first cataract, and thence emerges 
upon an unobstructed course to the sea. 
It is the valley below the first cataract which constituted Egypt 
proper. The reason for the change which here gives the river a free 
