﻿Vol. 66.~\ THE GEOLOGY OF XYASALAND. 215 



The Middle Group is formed of very thickly-bedded sandstones, 

 often hardened through silicification, and thus giving rise to 

 prominent scarp-features. Interbedded with these are several 

 bands of shales and flags, the former being sometimes very carbon- 

 aceous and containing ill-preserved plant-remains. It is probably 

 from this group that Drummond identified macrospores of lycopods : 

 while some miles away from the present section we have found 

 coal-seams with recognizable fronds of Glossopteris. 



The Upper Group comprises thickly-bedded yellow and grey mud- 

 stones with fine-grained grits, a few sandstones, and grey (occasion- 

 ally blue) shales. These crop out in the steep scarp right up to 

 the top of Mount Waller. The Upper Group, apart from this 

 section, is also found in low-lying ground round Lion Point. 



Comparing the above-described groups with those of Nkana and 

 Mpata, we find that in all these areas a central division charac- 

 terized by coal or shale is developed. So far, the comparison is 

 clear. If, however, we examine the Upper Group, say of Mpata, 

 we find that this is composed of grits followed by limestones and 

 mudstones, constituting the Drummond Beds. No limestones are 

 known in the Mount Waller area, but the various members of the 

 Upper Group are often distinctly calcareous, and so the divergence 

 is rather apparent than real. Finally, the Lower Sandstones of 

 Mount Waller seem thicker and coarser in grain than their northern 

 equivalents ; but a complete coincidence is not to be expected in 

 areas so widely separated, and, on the whole, the Mount Waller 

 beds may be held to fall into line with those of other areas in 

 Northern Nyasaland. 



(F) Henga Area. — Karroo rocks are found some little distance 

 to the south of the Mount Waller district, and constitute the 

 floor of the Upper Henga Valley. This depression runs roughly 

 north and south between the Nyika Plateau and the Vipya 

 Mountains, and slopes southwards to meet the wide trough-shaped 

 valley of the Southern Rukuru River. The Rukuru, just below 

 the junction, enters a gorge and so passes through the Vipya 

 Mountains to the lake (figs. 1 & 2, pp. 191 & 193). 



The Karroo of the Upper Henga appears to form a narrow 

 syncline, pitching south-westwards and truncated on the east and 

 west by trough-faults. The northern junction with the gneiss is 

 also faulted, but the southern boundary is ill-defined, for the 

 ground is greatly obscured by wash or by the alluvium of the 

 Rukuru River. A small isolated patch of mudstone is, however, 

 found in the Lower Henga or Rukuru Valley ; and it is possible 

 that the Karroo extends under the alluvium to as far south as the 

 junction of the Kasitu with the main river, or perhaps into the 

 Kasitu Valley itself. 



The rocks of the Upper Henga consist of calcareous mudstones, 

 with bands of grit, which evidently belong to the upper group of 

 beds in the neighbouring area of Mount Waller. 



