﻿208 



MESSKS. A. E. ANDREW AND T. E. G. BAILEY [May I9IO, 



west, by a horseshoe ring of hills composed of crystalline rocks. 



The two depressed areas of Karroo are connected by the Mwapo 



stream, which breaks through the dividing-ridge in a narrow gorge. 

 Yet a third depression occupied by rocks of Karroo age occurs on 



the south-west, and forms the drainage-basin of the Sere River, 



another tributary of 

 Fig. 5. the Eukuru. It is 



bounded on the 

 south by the high 

 Kayuni Range of 

 mountains, and on 

 the north by a long- 

 ridge of gneiss. 



The Karroo of the 



Mwapo and Sere 



River Area. 



Virauli Mtv 



The three districts 

 in which Karroo 

 rocks occur consti- 

 tute respectively the 

 Mwapo and Rukuru 

 trough, the Upper 

 Mwapo basin, and 

 the Sere basin. The 

 general dip of the 

 Karroo in the first 

 of these districts is 

 in an easterly direc- 

 tion, at an average 

 angle of perhaps 

 15°. The junctions 

 with the surround- 

 ing gneiss are, in 

 nearly all cases, 

 faulted ones. The 

 most important fault 

 runs along, and 

 practically coincides 

 with, the western 

 slope of the Rukuru 

 Ridge. This is 

 marked in places by 

 a line of flinty crush-roc]f which has undergone later brecciation 

 and silicification, and is associated at times with a broad vein of 

 calcite. Other important faults occur along the junction of the 

 gneiss and the Karroo, round Virauli Mountain and elsewhere. 

 The beds near these faults are frequently tilted at high angles. 



The only exception to the rule of faulted junctions is found 

 south-west of Virauli, where the basal beds of the Karroo rest 

 unconformably upon the gneiss. These beds consist of sandstones, 

 conglomerates, and boulder-beds, and are followed by the Middle 

 Shale Group, consisting of dark-grey argillaceous grits, gritty 



AKafiuni ML 



% 



f 





^0 



I' 1 ' 1 ' 1 







d 









•r-t 





P 



*m 



[.Scale.: I inch 

 - 3 Miles2 



Faults. 

 'Limestone Gcoup. 



Upper Sandstones. 

 Basement CongJom. 

 and Shale Group- 



