m 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:--]

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. These cracks afford a good idea of
the effect of the rains: the partial thunder-showers of October,
November, December, and even January, produce no effect on them; it is
only when the sun begins to return from his greatest southern
declination that the cracks close their large lips. The whole sponge
is borne up, and covers an enormous mass of water, oozing forth in
March and April forming the inundations. These floods in the Congo,
Zambesi, and Nile require different times to reach the sea. The bulk
of the Zambesi is further augmented by the greater rains finding many
pools in