NATURAL HISTORY OF AFRICA. 437 
of these and other minerals, collected in Africa, 
are now in the Museum of the University of Edin- 
burgh, presented by Mr Campbell, the Missionary 
traveller. I have much pleasure in mentioning 
this circumstance, as it shews that these gentle- 
men may execute all their important duties, while, 
at the same time, by their observations and col- 
lections, they contribute, in an eminent degree, tQ 
the advancement of Natural History. 
17* Fluor Spar. — A beautiful green coloured 
variety of this mineral, which has been confounded 
with emerald, is said to occur in the Island of Eme- 
ralds, in the Red Sea, 
18. Heavy Spar, or Sulphat of Barytes. — This 
mineral occurs in small quantity in Lower Egypt. 
19. Nitre. — This salt occurs incrusting rocks in 
Darfur, and in the Karroo deserts in Southern 
Africa. 
20. Natron.— Of this salt there are two subspe- 
cies, viz. common and radiated, and both are found 
in Africa* The common natron occurs in consi- 
derable quantity in Egypt, at the town of Nitria, 
also in the valley of the Natron Lakes, and in Nu- 
bia. * The radiated subspecies is found in the pro- 
vince of Sukena, two days' journey from Fezzan. 
It is found at the bottom of a rocky mountain, 
forming crusts, usually the thickness of a knife, 
* Glauber salt is associated in layers with the natron of 
the lakes. 
