Serers, and other Gambian tribes proper, probably exceed twenty thousand souls. Of these some fifteen thousand reside within the British territory, which comprises a group of fluvial islands and peninsulas with a total superficial extent of not more than 70 square miles.

Of all the streams rising in Futa-Jallon, by far the most copious is the Gambia, which drains nearly the whole of the central mass, Eastwards the main branch

Fig. 73. — Sources of the Dimma and Comba.

encircles the loftiest summits, while on the west and north-west another branch, the Grey River of the English, collects nearly all the rainfall. Thus the head-streams of the Senegal and Niger, as well as those of the Geba, Rio-Gande, Cassini, and Kakrima, flowing farther south direct to the coast, derive their supplies mainly from the less elevated southern and south-western slopes.

The sources of the Gambia, which have been visited by Hecquard, Bayol, and