the other rivers
in Africa together. It is second among the world's rivers, and the dark
detritus it carries to the Atlantic has been distinctly traced on the
ocean bed for six hundred miles from the land. Some geographers still
believed thirty years ago that all the waters of its upper basin might
be tributary to the Nile. Map-makers have been kept very busy recording
discoveries on the Congo. About one hundred explorers, some of them
missionaries and many employees of the Congo Free State, have mapped the
whole basin along its water-courses, and discovered the ultimate source
of its main stream. Our ideas of the hydrography of this great basin
have been revolutionized since Stanley, second only to Livingstone among
the great African explorers, in 1877 revealed the course of the
main river.

On his map, for example, he showed the southern tributaries as probably
flowing nearly due north; but all except one of these rivers rise in the
east and flow far to the west. When Wissmann was sent to the Upper
Kassai to follow it to the Congo, he was greatly surprised to find
himself floating westward week after week. When he reached the Congo a
steamboat was waiting for him at Equatorville, two hundred miles further
up the river, where he was expected to emerge. Schweinfurth believed the
Welle Makua flowed north to Lake Chad on the edge of the Sahara;
seventeen years later, after six or seven explorers had tried to solve
the problem, the river was found to be the upper part of the Mobangi
tributary of the Congo, larger than any rivers of Europe, excepting the
Volga and Danube. While Stanley was for five years planting his stations
on the Congo, he knew nothing of this great tributary, 1,500 miles long,
whose mouth was hidden by a cluster of islands which his steamers
repeatedly passed. Missionary Grenfell, on his little steamer, was
ascending the Congo one day, when accidentally he got into the mouth of
the Mobangi and went on for one hundred miles before he discovered that
he had left the main river. Few explorers have unwittingly stumbled upon
so rich a geographical prize.

While exploratory enterprises have been centred largely in tropical
Africa, no part of the continent has been neglected. We now know that
large areas of the Sahara are underlaid by waters which need only be
brought to the surface to cover the desert around them with verdure;
that most of the rain falling on the south slopes of the Atlas Mountains
sinks in