394 
GEOGRAPHICAL SYSTEMS, 
by the irruption of a new power, which chang- 
ed entirely the aspect of this continent. The 
descendants of Mahomet spread their empire as 
far as the ocean, and estabh'shed one of its grand 
seats in Northern Africa. This remarkable peo- 
ple, accustomed in their native seats to all the 
modes of carrying on trade over-land, and through 
deserts, were well calculated to overcome the ob- 
stacles which nature here presented on a still 
greater scale. Their caravans soon formed routes 
across the wide expanse of the African desert ; 
the banks of the Niger were not only explored, 
but colonized ; and the whole tract of central 
Africa, so far as known, became subject to Ma- 
hometan masters. The geographers, therefore, 
who arose during the flourishing era of Arabian 
science, had very ample opportunities of becom- 
ing acquainted with this part of the continent. 
They have left, accordingly, fuller descriptions 
than the ancients of the known parts, and have 
adopted, with regard to the unknown, an entirely 
different train of hypothesis. While Herodotus, 
Mela, and Pliny, made the central river of Africa 
run towards the east, and fall into the Nile, the 
Arabians, on the contrary, supposed it to flow 
westward from a common source with that river. 
To both they applied the common name of Nile ; 
one being the Nile of Egypt, and the other the 
Nile of the Negroes. Gana, situated upon the 
