646 FOSSIL TREES. 



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 great ancient river which flowed to the lake at Boochap 

 took this course exactly, and probably flowed thither until the fis- 

 sure of the falls was made. 



This flood having filled the river, we found the numerous rivu- 

 lets which flow into it filled also, and when going along the Zam- 

 besi, we lost so much time in passing up each little stream till 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 southeast. 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 (Sciiims cepapi) 

 had placed a great number of fresh leaves over a store of seed. 

 It is not against 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 silicified trees are met with 

 lying on the ground all 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 semidiameter 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 iron, and the pores filled with pure silica. 

 These fossil trees lie upon soft gray sandstone containing 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 imbedded exactly 

 like those now seen on the sea-beach, but I never could find a 

 shell. There are many nodules and mounds of hardened clay 

 upon it, which seem to have been deposited in eddies made round 

 the roots of these ancient trees, for they appear of different colors 

 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 ge- 

 ological structure of the country with interest, because here, it has 

 been stated, there once existed silver mines. The general rock is 



