In other parts of Africa valuable work was being done. David Livingstone was always a missionary first, but his explorations form a nobler memorial than those of any other African traveller. He had been working in Africa since 1840; in 1849 he crossed the Kalahari desert, and reached Lake Ngami; and in 1852 he started on a great journey up the Zambezi, discovering the Victoria Falls, and crossing to the west coast; and returning followed the Zambezi to its mouth on the east coast, thus taking the first steps to fill a great blank which had previously existed on the map of Africa. Between 1858 and 1864 he did much good work in the exploration of Lake Nyasa and the lower Zambezi, and incidentally made splendid efforts to stop the trade in slaves which was still carried on in that region. But it is his last journey, which took the form of an expedition to discover the watershed between Lake Nyasa and Lake Tanganyika, that is of paramount interest from the geographical standpoint. He started from Zanzibar in 1866; and, in spite of continual and serious illness, he travelled from Lake Nyasa to Lake Tanganyika, discovered lakes Mweru, Mofwa, and Bangweulu, and also the river Lualaba, which he took for the upper part of the Nile. He was cheered and encouraged by meeting with H. M. Stanley in 1871, who had been sent out to him with money and servants; but in 1873 he died, worn out by his constant travels, and still searching for the “fountains” which he believed to form the ultimate source of the Nile.