438 NATURAL HISTORY OF AFRICA* 
7« Syenite. 
This rock, which is distinguished from granite 
by the hornblende it contains as an essential in- 
gredient, occurs in beds along with porphyry, 
granite, and other rocks in Upper Egypt, and 
extends southward into Abyssinia. Captain 
Tuckey mentions it as one of the rocks he met 
with on the banks of the Congo. 
8. Greenstone, 
Greenstone, which is a compound of horn- 
blende and felspar, occurs in beds in Upper 
Egypt. It is sometimes porphyritic, and fre- 
quently it has an uniform green coloured basis, 
in which pale green crystals of felspar are imbed- 
ded, forming a beautiful rock, described under 
the name green porphyry. It is known to artists 
tinder the name antique green porphyry ; and it 
has been frequently confounded with the verd 
antique, which is a mixture of serpentine and 
marble, and therefore a very different rock from 
porphyry. 
9. Serpentine, 
This green coloured rock occurs in beds in 
mountains to the west of the Nile, where it al- 
ternates with beds of limestone and clay slate. 
It is also met with in the mountains that range 
