I travelled in Lunda, when the sponges were all supersaturated.  The grassy sward was so lifted up that it was separated into patches or tufts, and if the foot missed the row of tufts of this wiry grass which formed the native path, down one plumped up to the thigh in slush.  At that time we could cross the sponge only by the native paths, and the central burn only where they had placed bridges:  elsewhere they were impassable, as they poured off the waters of inundation:  our oxen were generally bogged—­all four legs went down up to the body at once.  When they saw the clear sandy bottom of the central burn they readily went in, but usually plunged right over head, leaving their tail up in the air to show the nervous shock they had sustained.

These sponges are a serious matter in travelling.  I crossed the twenty-nine already mentioned at the end of the fourth month of the dry season, and the central burns seemed then to have suffered no diminution:  they were then from calf to waist deep, and required from fifteen to forty minutes in crossing; they had many deep holes in the paths, and when one plumps therein every muscle in the frame receives a painful jerk.  When past the stream, and apparently on partially dry ground, one may jog in a foot or more, and receive a squirt of black mud up the thighs:  it is only when you reach the trees and are off the sour land that you feel secure from mud and leeches.  As one has to strip the lower part of the person in order to ford them, I found that often four were as many as we could cross in a day.  Looking up these sponges a bird’s-eye view would closely resemble the lichen-like vegetation of frost on window panes; or that vegetation in Canada-balsam which mad philosophical instrument makers will put between the lenses of the object-glasses of our telescopes.  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:—­]