* 
196 Transactions of the Boyal Society of South Africa. 
and the beds are, in part, spotted. Here the surface of the ground is 
covered with fragments of grit, spotted slate (much weathered) and granite, 
together with fragments of a quartz-tourmaline rock also from the granite 
area. 
Descriptions of Thin Sections of Rocks of this Series. 
141 W. Macro : A dark-coloured, banded rock, extremely fine-grained and 
containing numerous small white spots. 
Micro : The rock is composed entirely of angular quartz grains 
and brown tourmaline. The spots are small aggregates 
of quartz grains, devoid of tourmaline. 
138 W. Macro : A dark blue-grey rock ; fine-grained and compact. 
Micro : In this section the rock is seen to be extremely fine- 
grained and spotted. The bulk of the rock is composed 
of angular quartz grains and biotite ; a little tourma- 
line is present. Under the high power the spots are 
seen to be composed chiefly of muscovite ; some of 
them, between crossed nicols, extinguish as one, others 
as two or more individuals. Enclosed in the muscovite 
are grains of a colourless mineral having both a lower 
refractive index and a lower bi-refringence than the 
mica ; the bi-refringence seems too high for either 
( juartz or cordierite. The grains are too small to allow 
for testing in convergent polarised light. The mineral 
may be andalusite. 
It is significant that in both these rocks there is no trace left of original 
argillaceous matrix. It is presumed that the much-weathered, spotted 
varieties are modifications of the more highly argillaceous beds of the series. 
3. The Granite of the Schapenberg. 
Extent of Outcrop and General Description. 
The granite not only constitutes, but is almost continually exposed over, 
the major portion of the Schapenberg ; it extends also into the lower lying 
and partly cultivated area to the south. Here it is largely covered with 
either soil or gravel and only isolated exposures serve to show its extension. 
One such exposure occurs about 150 yards above the Caledon Eoad as one 
approaches Water Kloof from Somerset West; a second occurs a little 
further on in the same direction, whilst at a point still further east, about 
three-(|uarters of a mile distant from where the Water Kloof stream crosses 
the road, the granite is exposed in the roadway. Just above the road at this 
place there arc small quarries in the granite. All these are exposures of a 
medium- grained grey granite which is described in detail below. Further 
to the south, and just to the north of the railway line, there is a low, stony 
