EXTENT OF THE PLATEAU. 
49 
accomplished. There is said to be none other like it 
on the road to Soudan, except a tremendous desert 
between Ghat and Aheer. However, we must not 
trouble ourselves about this as yet. 
As for the Hamadah, we know^ that near Sokna 
the plateau breaks up and forms what are called the 
Jebel-es-Soudy, or Black Mountains, a most pic- 
turesque group of cliffs ; and again on the route to 
Egypt from Mourzuk, six days' journey south-east 
from Sokna, it also breaks into huge cliffs, and bears 
the name of El-Harouj. These mountain buttresses 
are either the bounds of the Hamadah, or masses of 
rock where it breaks into hills, forming ravines or 
valleys. But, in fact, how far the Hamadah extends 
between Ghadaraez on the west and Augila on the 
east is not yet properly ascertained. It seems to be 
like a broad belt intercepting the progress of com- 
merce, civilisation, and conquest, from the shores of 
the Mediterranean to Central Africa. The kingdom 
of Fezzan, however, advances like a promontory 
beyond it ; and then on every side stretches the 
desert ocean with its innumerable oases or islands, 
wdiich, from being once mere fluctuating names, as 
it were, on a guess map, are now by degrees dropping 
one by one into their right places. 
On the breaking-up of the plateau we observed 
its geological structure to consist of three principal 
strata : first, a covering or upper crust, limestone 
with flints and red earth ; then masses of marl ; and 
then sandstone, lumps and masses of which were 
VOL. I. E 
