418 Proceedings of the Royal Physical Society. 
changed. It will be seen in the sequel what conditions to 
a great extent produce this change in character, and in the 
Tropics a change in physical stamina, likewise. It will not 
be possible, however, for me to apply the facts I allude to 
in this connection. My scope is a more limited one, but 
I have thought it well to call attention to the subject 
because of its great importance. 
Looked at in the light of modern geology, Africa is of 
creat antiquity. The origin of the continent belongs, doubt- 
less, to Archeean, Palzeozoic, and early Mesozoic eras. In round 
numbers the continent has an area of 9,858,000 geographical 
square miles, its length is 4330 geographical miles, and its 
breadth about 5000 miles. It is situated between latitude 
37° 20’ 40” N. and latitude 34° 49° 15” S. The coast-line is 
remarkable; it is only some 17,700 miles in length. This is 
out of proportion to its vast area, and is due to the absence 
of bays, inlets, or estuaries. The configuration of the continent 
of Africa is peculiar. It may be described as possessing a 
coastal girdle, having a varying breadth of from 100 to 
300 miles in width. This girdle bounds an enormous 
plateau, which slopes from the east towards the west, and 
in the main axis of which, running from §.W. to N.E; 
there is a range of mountains, broken, it is true, at intervals. 
The main elevation of the continent is less than that of 
Europe or Asia; an oblique line drawn from Loanda to 
Suakim passes through a table-land varying in height from 
3000 to 4000 feet. It is remarkable that the three great 
rivers—the Nile, the Congo, and the Zambesi—have their 
headwaters almost together, so low is the watershed; and 
the whole river system of Africa renders ready drainage 
impossible, and thus gives to it, on the whole, a water-logged 
character, especially in vast areas in the centre of the 
continent. It is noteworthy that there are six drainage 
areas in Africa, three inland—the Sahara Desert, the 
Kalahari Desert, and Eastern Abyssinia—and then the 
. Atlantic Ocean, the Mediterranean Sea, and the Indian 
Ocean,— the drainage area towards the Atlantic Ocean, includ- 
ing as it does the river systems of the Niger and the Congo, 
being the greatest. With the exception of the Nile, whose 
