Great Dijke of Noriie of Soutliern Bliodesia. 
9 
thickly wooded rectilinear range a mile to two miles wide. This forms 
one continuous flat range from the Walsh farm Block to Edward's farm, 
where there is a gap in the hills occupied by pyroxenite and peridotite. 
From Helvetia farm northwards the range is more rugged. It narrows 
on Shikupa farm and on Unki splits into two arms, the easternmost 
continuing as a strong feature of peaked hills, but the western arm, owing 
to interruptions of peridotite and pyroxenite in the low ground, becomes 
very broken for a few miles until on Paarl it reunites with the eastern 
arm and continues northwards again as a wide flattish-topped range. 
The range is bounded on either side by the enstatite-pyroxenites. 
In very few instances small detached bodies of the felspar-rich norite 
may be noted. There are small boss-like bodies lying in enstatitite at the 
foot of the Selundi range on Ortner's farm and in the large vlei in the 
middle of the Great Dyke east of the Wanderer Mine. 
The rock usually weathers into small round blocks, but the summits 
of the hills show huge jointed blocks and occasional crags. 
The rock is a very characteristic type. It is medium- to somewhat 
coarse-grained, granitic textured, and mottled grey and white. The 
constituents are easily recognized in hand specimens. They are a white 
or glassy striated felspar generally exhibiting crystalline form (short 
striated laths) with interstitial pale leek-green or grass-green and brownish 
semitransparent pyroxenes, which in most specimens are typically of 
irregular shape, being interstitial to the felspar, but in other rocks of a 
more granular nature it forms well-shaped prismatic crystals, and in still 
others (see Plate I EI, fig. 3) strikingly poikilitic on a small scale. The 
constituents are almost invariably evenly distributed, but in some places 
they are irregularly segregated and poikilitic, somewhat as in certain 
•of the Canadian anorthosites (see figure, Adams, Geological Sicrvej/, 
Canada, Annual Report, vol. viii., 1895, p. 104 J). A red-brown mica 
and pyrites (pyrrhotite, pyrite, and chalcopyrite) are fairly constant 
accessories occurring in small quantities. The sulphides are never in 
idiomorphic crystals, but like the pyroxene are interstitial to the felspar. 
There is no doubt in the writer's mind as to the sulphide being an original 
constituent of the rock. A trace of green hornblende was noted in one 
slide and minute quantities of calcite, zoisite, chlorite, bastite, and 
magnetite in others. 
The felspar ranges from basic labradorite to acid anorthite, but usually 
is bytownite or labradorite, a small quantity of less basic felspar (? ande- 
sine) is also present in some rocks. The felspar (see Plate III, hg. 1) 
averages 70 per cent, of the volume of the rock, but ranges from 64-75 
per cent, as determined by Sorby's method [drawing on squared paper 
with camera lucida several fields of a thin section, the outlines of the dark 
constituents being represented. The percentage then computed by count- 
