Chap. XXIX. 
FOSSIL TREES. 
603 
identical with, that of the Nile. It would not be influenced by 
any streams in the Kalahari, for there, as in a corresponding part 
of the Nile, there would be no feeders. It is to be remembered 
that the gTeat ancient river which flowed to the lake at Boochap 
took this course exactly, and probably flowed thither until the 
fissure of the falls was made. 
This flood having filled the river, we found the numerous rivu¬ 
lets which flow into it, fiUed also, and when going along the Zam¬ 
besi, we lost so much time in passing up each little stream tfll 
we could find a ford about waist-deep, and then returning to the 
bank, that I resolved to leave the river altogether, and strike 
away to the S.E. We accordingly struck off when opposite the 
hill Pinkwe, and came into a hard Mopane country. In a hole 
of one of the mopane-trees, I noticed that a squirrel (Sciurus 
cepapi) had placed a great number of fresh leaves over a store 
of seed. It is not agamst the cold of winter that they thus lay 
^ up food, but it is a provision against the hot season, when the 
trees have generally no seed. A great many sihcified trees are 
met with lying on the ground aU over this part of the country; 
some are broken off horizontally, and stand upright; others are 
lying prone and broken across into a number of pieces. One was 
4 feet 8 inches in diameter, and the wood must have been soft 
like that of the baobab, for there were only six concentric rings 
to the inch. As the semi-diameter was only 28 inches, this large 
tree could have been but 168 years old. I found also a piece of 
palm-tree transformed into oxide of fron, and the pores filled with 
pure silica. These fossil trees lie upon soft grey sandstone con¬ 
taining banks of shingle, which forms the underlying rock of the 
country all the way from Zumbo to near Lupata. It is met with 
at Litubaruba and in Angola, with similar banks of shingle im¬ 
bedded exactly hke those now seen on the sea-beach, but I never 
could find a shell. There are many nodules and mounds of hard¬ 
ened clay upon it, which ^eem to have been deposited in eddies 
made round the roots of these ancient trees, for they appear of 
different colours in wavy and twisted lines. Above this, we have 
small quantities of calcareous marl. 
As we were now in the district of Chicova, I examined the 
geological structure of the country with interest, because here, it 
has been stated, there once existed silver-mines. The general 
