438 NATURAL HISTORY OF AFRICA. 
and sometimes, although rarely, of an inch, on the 
surface of the earth. According to Mr Barrow, it 
would appear also to occur in the district of Tarka, 
in Bosjesman's Land, in Southern Africa. 
21. Sidjjhur. — This substance is met with in 
Darfur. 
22. Graphite or Black Lead. — It is said to oc- 
cur near the Cape of Good Hope, and also near 
Tunis. 
23. Gold. — Tin's continent affords a consider- 
able quantity of gold, which is always obtained in 
the form of dust or rolled masses, and is found 
in the sand of rivers, or the alluvial soil of valleys 
or plains. The northern parts of Africa afford 
but little gold, but in the middle and southern 
regions, there are several tracts remarkable for the 
quantity of gold they afford. The first is Kor- 
dofan, situated between Darfur and Abyssinia. 
The gold collected there is brought to market by 
the negroes in quills of the ostrich and vulture. 
This territory, it would appear, was known to the 
ancients, who regarded ^Ethiopia as a country rich 
in gold. 
The second principal tract lies to the south of 
the Great Desert of Zahara, and in the western part 
of Africa. The gold is collected in that extensive 
flat which stretches from the foot of those moun- 
tains in which are situated the sources of the 
rivers Gambia, Senegal, and Niger. Gold is also 
