of Edinburgh, Session 1869 - 70 . 131 
vast river cannot be formed in a short course, but must have its 
rise far in the interior of the continent. 
If we take the Kassabi river and its drainage to the Nile, where 
shall we find a sufficiently lengthened course for the Congo? 
Tuckey’s unelaborated notes give the opinion that the “extraordi- 
narily quiet rise of the river shows it to issue from some lake, which 
had received almost the whole of its waters from the north of the 
line;” and again, he says, “ I cannot help thinking that the Congo 
will be found to issue from some large lake or chain of lakes, con- 
siderably to northward of the equator.” The reason of Tuckey’s 
supposition that the lakes, which evidently maintain the volume 
of water in the Congo, would be found north of the equator, is 
this, that he found the rising of the river beginning on the first 
days of September. At the time of his journey little or nothing 
was known of the times of the rainy seasons in Central Africa 
from actual experience. Since then the traveller Burton has told 
us (in his account of the expedition to Tanganyika, R. Gr. S. 
Journal, vol. xxix.), that in the latitude of Tanganyika the rain 
sets in at the end of August, lasting till May; and Livingstone 
says, in his latest letter, that he did not proceed to Lake Bangweolo 
from the Cazembe’s capital, where he arrived about the middle of 
September, because the rains had set in. Lake Ulenge lies between 
these latitudes, so that the rise of the waters of the Congo on the 
first of September is perfectly explainable without the necessity of 
taking its reservoir lakes to the north of the equator ; if the lakes 
were there, the rise of the Congo would occur at a much earlier 
period of the year, as we shall afterwards notice, and, indeed, the 
space in which Lake Ulenge lies, seems to be the only one on the 
continent whose rainy season would agree with the observed rise 
of the Congo. 
3. The Physical Features of the Lake Legion and the Lakes. 
The great highlands of the world encircle and turn their steepest 
verge towards the Pacific and Indian Oceans ; the slope is gentle 
towards the great plains which surround the Atlantic and Arctic 
Seas. Africa is no exception to this rule, since it presents to the 
Indian Ocean the abrupt descent of the plateau which extends 
along its eastern side from the Cape Colony to Abyssinia, north- 
