Vol. 63.~] GEOLOGY OF THE ZAMBEZI BASIN. 175 



progress among the superficial formations of the plateau. The 

 thin band of peculiarly indurated shale, apparently silicified, 

 upon the lower sandstone in the second section (Bed 4, Section 3) 

 is probably a further result of the same process. Another rock 

 of unusual aspect associated with this sandstone is the ferruginous 

 claystone, which is sprinkled with concretionary spherules of deep-red 

 haematite, about the size of large oolite-grains and having a radial 

 structure internally. 



In colour, the sandstones vary from dull-red to pale yellowish- 

 grey, the paler tints predominating. While some beds are marked 

 by distinctive tints, there is also in places a mingling of the red 

 and grey tints in the same bed. Both in colour and texture, these 

 sandstones recall the characters of the familiar English Bimter 

 Sandstones ; and the likeness becomes accentuated in the pebbly 

 beds occurring in the higher part of the series, the pebbles having 

 the same thoroughly rounded outlines and the same scattered 

 distribution as in the pebbly sandstones of the Bunter. This 

 similarity I noticed especially in the steep kopje at 'Mtoro's Kraal. 



The thicker sandstones are strongly jointed, one set of joints 

 striking east-and-west like those of the basalt-country, with other 

 cross -joints striking approximately north- and-south. In the 

 stream-beds, the rock is sometimes eroded along these joints into 

 deep crevices ; as, for example, in a dry stream-bed 3 or 4 miles 

 west of Wankie, where one crevice of this kind, which crosses the 

 stream-bed at right angles, is 8 or 10 feet deep and not more than 

 2 feet wide. On the top of the kopjes, these jointed sandstones 

 often weather into huge blocks of fantastic outline ; and in the 

 precipitous krantzes the scaling away of the rock along the joints 

 gives a botryoidal aspect to the exposures. 



Prom the remarkable scantiness of superficial covering, which 

 characterizes the whole region except in the sand-bults and loam- 

 flats, the sandstones crop out in many places in absolutely bare 

 platforms of wide extent, but with numerous bushes and trees 

 rooted in the crannies ; and in this manner the weathering and 

 subsequent erosion along the crevices is evidently facilitated. 

 One of these bare platforms, about a mile east of Wankie, was 

 curiously pitted with hollows, and also contained, embedded in its 

 surface, a few small lumps of silicified wood, not rooted like trees 

 but looking as if derived in their present condition from some older 

 deposit. The pittings appeared to be the casts of similar lumps 

 which had been removed. 



Some blocks of silicified wood of the same character were found 

 lying loose, along with a sprinkling of quartz -pebbles, on the 

 surface of the basalt adjacent to a bold ridge of sandstone, in the 

 Deka basin, 6 miles east-north-east of our Bumbusi camp, one 

 being a segment of a stem 15 inches in diameter, showing a well- 

 marked core ; and these blocks, like the accompanying pebbly 

 detritus, have no doubt been derived from the sandstone. 



Near the place where the lowermost sandstones abut upon 

 the previously described spur of ancient schistose rocks south of 



