The flat, or nearly flat, tops of the subtending and transverse ridges of this central country give rise to a great many: I crossed twenty-nine, a few of the feeders of Bangweolo, in thirty miles of latitude in one direction.

Burns are literally innumerable: rising on the ridges, or as I formerly termed them mounds, they are undoubtedly the primary or ultimate sources of the Zambezi, Congo, and Nile: by their union are formed streams of from thirty to eighty or 100 yards broad, and always deep enough to require either canoes or bridges.

These I propose to call the secondary sources, and as in the case of the Nile they are drawn off by three lines of drainage, they become the head waters (the _caput_ Nili) of the river of Egypt.
Thanks to that all-embracing Providence, which has watched over and enabled me to discover what I have done.

There is still much to do, and if health and protection be granted I shall make a complete thing of it.
[Then he adds in a note a little further on:--] But few of the sponges on the watershed ever dry; elsewhere many do; the cracks in their surface are from 15 to 18 inches deep, with lips from 2 to 3 inches apart.

Crabs and other animals in clearing out their runs reveal what I verified by actually digging wells at Kizinga and in Kabuire, and also observed in the ditches 15 feet deep dug by the natives round many of their stockades, that the sponge rests on a stratum of fine white washed sand.