This process is still going on, though more slowly.  The mapping we see of Lake Tanganyika, one of the longest lakes in the world, has been in use for seventeen years since missionary Hore made his boat journey of one thousand miles around its coasts, but the new map of the Moore expedition now being introduced gives the main axis of the lake a more northeast and southwest direction.  The Hore map has met the fate that usually overtakes the early surveys of every region.  It rendered good service as long as it was the best map; but the Moore expedition had first-rate appliances for computing longitudes, and as Captain Hore lacked these, it is not strange that his map has been found to be defective.

The world has been treated to many geographical surprises in the course of this incessant transformation of the map of the continent.  Many of us may remember in our school geographies, the particular blackness and prominence of the Kong Mountains, extending for two hundred miles parallel with the Gulf of Guinea.  They were accepted on the authority of Mungo Park, Caillie, and Bowditch, all reputable explorers who had not seen the mountains, but believed from native information that they existed.  The French explorer, Binger, in 1887 sought in vain for them.  Later explorers have been unable to find them.  They are, in fact, a myth, and will be remembered chiefly as a conspicuous instance of geographic delusion.  It had long been supposed that the navigation of the Niger River, the third largest river in Africa, was permanently impaired by the Bussa Rapids, about one hundred miles in length, where Mungo Park was wrecked and drowned.  But Major Toutee, a few years ago, when assailed by hostile natives, made a safe journey with his boats through the rapids; and Captain Lenfant, in 1901, carried 500,000 pounds of supplies up the river and through the rapids to the French stations between Bussa and Timbuktu.  He had a small, flat-bottomed steamboat and a number of little boats propelled by fifty black paddlers.  He says that by the land route he would have required 12,000 porters, and they would have been one hundred and thirty days on the road.

It was believed that a land portage would always be necessary between the sea and the Zambesi, above the delta, till 1889, when Mr. Rankin discovered the Chinde branch of the delta, so broad and so deep that ocean vessels may ascend it and exchange freight with the river craft.

It has been found that more water pours into the ocean through the Congo’s mouth, which is six miles wide, than from all 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.