The Granite Area of the ScJmpenherg, Som,erftet West. 197 
kopje formed of an extreme modification of the granite. This exposure 
apparently marks the end of the southern extension of the granite outcrop. 
To the south lies a broad alluvial plain extending to the sea (False Bay). 
Although no actual continuity can be traced between these various exposures, 
they have been regarded as portions of a continuous mass and mapped as 
such ; this is in accordance with the interj^retation of the late Greological 
Commission of the Cape of Good Hope.* As a general rule the limit of the 
granite can only be inferred from the presence of grit fragments on the 
surface. The greatest length of the outcrop is from north to south and is 
approximately 2 miles. The greatest breadth, from east to west, is about 
li miles. 
Generally speaking, the granite forms very rugged country. At the 
surface, and frequently to a great depth below, the rock is much decomposed, 
so that it is a difficult matter to procure unweathered specimens. Essentially 
the rock is a grey, porphyritic granite, of which two distinct kinds occur 
which differ only in texture ; the one is medium -grained with phenocrysts of 
felspar and quartz ; the other is fine-grained — microcrystalline — containing 
phenocrysts of quartz, felspar, and biotite, and should be regarded either as 
a quartz porphyry or, more correctly, granite-porphyry. Very commonly 
surfaces have a coarse, grit-like appearance and are frequently studded with 
the felspar and quartz phenocrysts. No regular disposition of the fine and 
medium-grained varieties with regard to the centre of the intrusion is 
apparent. Along portions of the margin — particularly on the north and 
north-east — the granite varies considerably both in texture and mineral 
composition. These variations are due in part to the contact with the sedi- 
mentary series, and in part to subsequent pneumatolytic action. Descrip- 
tions are given of these altered granites below. Veins of black tourmaline 
and veins consisting of parallel bands of quartz and tourmaline, traverse the 
granite throughout a large part of the area ; they generally strike from 
about 10° N. of E. to 10° S. of W. In addition to these quartz- 
tourmaline veins numerous roughly spherical, dark-coloured patches varying 
from 1 in. to 2 in. in diameter, and composed largely of black tourmaline, 
occur throughout the fine-grained granite porphyry. Shear planes are occa- 
sionally encountered running in the same direction as the quartz -tourmaline 
veins ; frequently — as, for example, on the summit of the spur to the east 
of Water Kloof ravine — the courses of these planes are marked by veins of 
milky quartz. In the locality cited above, on each side of the quartz veins 
is sheared granite traversed by numerous veinlets of milky quartz. The 
shearing has, apparently, only affected a narrow strip of granite. The 
erosion of Water Kloof most probably commenced along one of these planes. 
Three pits have been dug at intervals near to the bed of the stream. From 
* Sheet 1, Cape Colony. 
