﻿Yol. 66.] ON THE GEOLOGY OF NTASALAND. 203 



The Karroo of the jS"kana area consists of sandstones, shales, lime- 

 stones, etc., and, except on the north, is bounded by faults, the most 

 important of which run in a roughly north-and-south direction. In 

 addition to the boundary-faults, there is also an important fault tra- 

 versing the sedimentary rocks in a north-easterly and south-westerly 

 direction, thus dividing the series into two parts. In the northern 

 part the rocks strike north and south, and dip eastwards at angles 

 which increase from 10° to 30° as the outcrops are crossed towards 

 the west. Close to the western boundary -fault the beds steepen, 

 and dip at 60° to 70°. In the southern part the strike is very 

 variable, but probably averages east-north-east in direction, the 

 beds dipping about 20° south-south-eastwards. 



The northern boundary of the Karroo as defined above is purely 

 arbitrary, for the same formation continues across the Songwe River 

 and has been described by Dr. W. Bornhardt. 1 



The beds composing the Xkana Series are, as follows, from the top 

 downwards : — 



Upper Division. Thickness in feet^ 



6. Striped Grits with Concretions ? 



5. Limestone Group 150 



4. Green Shales and Purple Grits 450 



3. Upper Sandstones 150 



Middle Division. 



2. Shale Group 60 



Lower Division. 



1. Lower Sandstones 700 



Total exceeding 1510 



(1) The Lower Sandstone Group is at least 700 feet thick,, 

 the lower 400 feet containing a great number of grey, red-grey, 

 and yellow hard flags with some fine-grained grits. The upper 

 300 feet consist of medium-grained felspathic sandstones, usually 

 grey but becoming pinkish on weathering. Towards the top. 

 occasional black shales are found. 



(2) The Shale Group is not well exposed in any section. Near 

 Katijoka's village, however, about 60 feet of mingled mudstones,. 

 clays, shales, fine-grained sandstones, and coals occur. Most of the 

 mudstones, clays, etc. are dark, owing to the presence of carbo- 

 naceous matter. In the coal-seams it is common to find cracks 

 at right angles to the bedding-planes, about 4 to 6 inches wide, 

 now tilled with felspathic sandstone. 



(3) The Upper Sandstones and Grits are somewhat more reddish 

 in tinge than the Lower Sandstones ; they are medium to coarse in 

 grain, very felspathic, and, like the Lower Sandstones, crumble readily 

 on the exterior after exposure. 



1 ' Deutsch Ost-Afrika vol. vii (1900) pp. 144, 150, Sec. 



