NATURAL HISTORY OF AFRICA. 431 
loured quartz, and does not contain organic re- 
mains. It is not improbable, that much of this 
sandstone may prove, on more particular examina- 
tion, to belong to the species named quartz rock, 
which occurs in vast beds both in the primitive 
and transition classes. 
Limestone. 
This limestone has a splintery or conchoidal frac- 
ture, and its colour is grey or variegated. It con- 
tains numerous petrifactions of shells, corals, and 
fishes. It extends from Syene to the Medi- 
terranean ; and in Lower Egypt reaches from 
Alexandria to the Red Sea, in the vicinity of Suez. 
It extends from the westward of the Nile onward 
to Fezzan, forming single hills and ranges of hills. 
In the hilly district of Fezzan, near Harutsch, the 
limestone which still prevails is caped and inter- 
mixed with trap rocks. The limestone is generally 
disposed in horizontal strata, but where the trap 
rocks appear, the stratification is more or less va- 
ried in its position. In travelling from Fezzan 
northwards towards Tripoli, the continuation of 
the Harutsch presents ranges of basaltic eminences 
alternating with rows of limestone hills. A lime- 
stone of the same description appears to view in 
the mountain ranges leading to Cosseir, and in the 
same tract of country there are hills of limestone 
associated with gypsum. It is also met with in the 
lower parts of the Atlas range, as near to Algiers, 
