“The discovery in the central portion of the Cape colony, by Mr. Bain, of fossil remains in a lacustrine deposit of secondary age, and the well-known existence on the coast of loftier mountains known to be of a Palæozoic or primary epoch and circling round the younger deposits, being followed by the exploration of the Ngami Lake, justified me in believing that Africa had been raised from beneath the ocean at a very early geological period; and that ever since that time the same conditions had prevailed. I thence inferred that an interior network of lakes and rivers would be found prolonged northwards from Lake Ngami, though at that time no map was known to me showing the existence of such central reservoirs. Looking to the west as well as to the east, I saw no possibility of explaining how the great rivers could escape from the central plateau-lands and enter the ocean except through deep lateral gorges, formed at some ancient period of elevation, when the lateral chains were subjected to transverse fractures. Knowing that the Niger and the Zaire, or Congo, escaped by such gorges on the west, I was confident that the same phenomenon must occur upon the eastern coast, when properly examined. This hypothesis, as sketched out in my ‘Presidential Address’ of 1852, was afterwards received by Dr. Livingstone just as he was exploring the transverse gorges by which the Zambesi escapes to the east, and the great traveller has publicly expressed the surprise he then felt that his discovery should have been thus previously suggested.”