NATURAL HISTORY OF AFRICA. 435 
formed by the action of the atmosphere and the 
water on previously existing rocks, it is of conse- 
quence to know accurately the oryctognostic and 
geognostic relations of sands, particularly those 
that form the great deserts in Africa and other 
quarters of the globe. 
MINERALS FOUND IN AFRICA. 
1. Topaz. — This gem is said to have been col- 
lected by the order of the ancient kings of Egypt, 
in an island in the Red Sea named Zemorget, or 
the Island of Topazes. 
2. Emerald. — The Romans are said to have 
procured this gem from the mountains situated on 
the western shores of the Red Sea in Upper Egypt 
and Ethiopia. Bruce mentions an island in the 
Red Sea named the Island of Emeralds, but which 
contains only green coloured fluor spar. 
3. Chrysoheryl. — This gem is also enumerated 
amongst the mineral productions of Upper Egypt. 
4. Schorl. — It occurs imbedded in the granite 
at the sources of the Senegal. 
5. Epidote or Pistacite. — This mineral is found 
in the valleys near Cosseir, along with actynolite, 
and also near Orange river in Southern Africa. 
6. Precious Garnet. — This beautiful gem is 
found in Ethiopia. 
7. Quartz. — The rarest varieties of quartz met 
