Ixxxiv 
APPENDIX. 
great body, or western division of this ocean, comprized between Fezzan 
and the Atlantic, is no less than 50 caravan journies across, from north to 
south ; or from 750 to 800 G. miles ; and double that extent, in length : 
without doubt the largest desert in the world. This division contains but a 
scanty portion of islands (or oases) and those also of small extent : but the 
eastern division has many ; and some of them very large. Fezzan, Gada- 
mis. Taboo, Ghanat, Agadez, Angela, Berdoa, are amongst the principal 
ones : besides which, there are a vast number of small ones. In effect, this 
is the part of Africa alluded to by Sirabo,* when he says from Cneius Piso, 
that Africa may be compared to a leopard's skin, I conceive the reason 
why the oases are more common here, than in the west, is, that the stratum 
of sand is shalloiver, from its surface, to that of the earth which it covers. In 
other words, that the water contained in that earth, is nearer to the surface; 
as in most of the oases it springs up spontaneously, t Can any part of the 
cause be assigned to the prevalent easterly winds, which, by driving the finer 
particles of sand to leeward, may have heaped it up to a higher level in the 
Sahara, than elsewhere ? + 
The springs, no doubt, have produced the oases themselves, by enabling 
useful vegetables to flourish, and consequendy population to be established. 
* Page 130. 
f Water is found at the depth of a few feet, in Fezzan ( Afr. Assoc. Q_ p. 96 : O. p. 
146). The same is said by Pliny, concerning this quarter of Africa ; lib. v. c. 5. But 
farther to the N W, on the edge of the Desert, and in the country of Wadreag in particu- 
'lar (Shaw, p. I35.)> wells are dug to an amazing depth, and water mixed with fine sand, 
springs up suddenly, and sometimes fatally to the workmen. The Doctor tells us, that 
the people call this abyss of sand and water, " the sea below ground." Exactly the same 
state of things exists in the country round London, where the sand has in several cases 
nearly filled up the wells. (See Phil, Trans, for 1797.) The famous well lately dug by 
Earl Spencer (at Wimbledon), of more than 560 feet in depth, has several hundred 
feet of sand in it, 
X Ships that have sailed at a great distance from the African coast, opposite to C, Blanco 
and C. Bojador, have had their rigging filled with fine sand, when the wind blew strong 
off shore. The accumulation of the Bissago shoals may have been partly owing to this 
cause also. They occupy the position where a great eddy of the general southerly current 
takes place, between C. Verd and Sherbro'. 
