146 NATURAL HISTORY OF 



AFRICA. 



Of Africa the most striking feature is the tabular form of its 

 structure, standing immovable, like a huge bulwark, almost 

 centrally beneath the equator, without a plentiful vegetation, — 

 almost without forests; with few undrained lakes, and, conse- 

 quently, few great rivers, which derive their supplies of moisture 

 from clouds coming from distant regions, and furnishing a 

 diminishing supply; for there is an acknowledged desiccation 

 in progress, observed alike in Morocco, at the Cape, and most 

 in Abyssinia. Perhaps the oldest of the continents, it appears 

 exhausted. With a vigorous animal or vegetable life, thinly 

 scattered, or confined to particular valleys, and with proofs of a 

 desert state so remote that no other region can produce a simi- 

 lar example, — namely, in the Baobabs (Adansonia digittata), 

 of ninety feet in circumference, a bulk so enormous as to 

 induce Adanson to assert that they contained full six thousand 

 rings of annual growth, — that is, an age which no other living 

 organic body on earth can claim.* In this great region, the 

 Nile alone, of all the rivers, is of ancient interest in what 

 relates to the History of Man. Though for centuries past little 

 or no addition has been made to the delta, the coast lakes have 

 materially decreased in depth, and the bed of the river is now 

 much higher than in antiquity, since the plain of Thebes 

 is, during inundations, in many parts under water. In Abys- 

 sinia, mountains, formerly covered with forests, are become 

 pasture lands ; and a large river, the Kibber, which descends 

 from the south-west side of that great mountain system, pro- 

 ceeds obliquely to the eastern coast, and is suddenly arrested 

 at its mouth, under the equatorial line, by a broad beach of 



* There are oaks in France, Switzerland, and even in Great Britain 

 above thirty feet in circumference, which may be 3000 years old. A 

 chestnut on Etna, not one of the largest or oldest, left a portion of a side 

 shoot, not containing- the inner core or circles, which, nevertheless, afforded 

 1700 rings of annual growth. Baobabs thriye best on arid plains. 



