﻿370 ME. FREDERIC P. MENNELL ON THE [Aug. I9IO, 



Umguza (sandstones overlying conglomerate and capped by basalt) ; 

 at Forest Yale and the hill on the opposite side of the railway 

 (false-bedded, white to pinkish or brownish sandstone resting upon 

 granite). The most important outlier is, however, that marked by 

 the conspicuous flat-topped hill known as Taba-s'Induna. This 

 eminence has a basaltic capping, absent from the rest of the outlier. 

 The basalt appears to be a lava-flow, and is of precisely similar 

 character to that of the Amanxele Hills. It appears to occur at a 

 lower horizon than usual, as the underlying beds are fine white 

 sandstone, instead of the higher red flaggy beds. This white sand- 

 stone is without any sign of bedding-planes, and even shows a kind 

 of spheroidal weathering in places. It resembles exactly the white 

 beds of the Cave Sandstone (Jurassic) of Cape Colony. The lowest 

 beds are apparently pinkish sandy shales resting upon schists. 

 North of Pasipas (already mentioned) the Forest Sandstones run 

 northwards without a break for nearly 150 miles. Beyond the 

 AVankie Coalfield the sandstones themselves make little show; but 

 the basalts, which are often seen farther south, here become of 

 .greater importance, and cover several thousand square miles around 

 the Victoria Falls. They are often highly amygdaloidal, and are 

 ■characterized by their glomeroporphyritic structure and by the 

 absence of olivine. 



(d) The Somabula Gravels and Sands. 



The gravels and sands of the Somabula Forest, about 12 miles 

 south-west of Gwelo, are of considerable interest for several reasons. 

 They are the only beds resembling the gravels of the ' drift ' deposits 

 of England in their lithological characters ; they afford the sole 

 development, other than purely superficial deposits, of sediments 

 overlying the Forest Sandstones ; and they are, moreover, remarkable 

 for the variety of gems and other interesting minerals which they 

 yield. 



These beds occur on a series of ridges near the apex of the main 

 watershed of the country, and have a thickness, where not reduced 

 by denudation, of about 150 feet. The uppermost beds are red and 

 white sands, which have only occasionally survived on the crests of 

 the ridges. Then come the gravels, composed of beautifully rounded 

 pebbles in a matrix of sandy clay, often ferruginous. Yein-quartz 

 is the commonest material among the pebbles, but a dark quartzite 

 of unknown origin is also common. Sections show development of 

 fibrolite in the interstitial material between the quartz-grains of this 

 rock, so that it had evidently been subjected to contact meta- 

 morphism, and it is just possible that the source is the Banded 

 Ironstone Series. Recognizable banded ironstone is fairly abundant, 

 and so is agate from the basalts of the Forest Sandstone Series. 

 The gravel has a maximum thickness of 40 or 50 feet. Below it 

 come white micaceous sands, sometimes including clayey bands. 

 The sands do not appear to contain many interesting minerals 

 among their coarser material: but from the gravels are obtained 



