12 
Transactions of tJte Boyal Society of South Africa. 
edge of the intrusion in a few places, e.g. near Secombi's Kraal to the 
north-west, about 1|- miles south of the Victoria road drift across the 
XJmtebekwe river, and east of the Little Tebekwe river onMakomisa farm. 
The rock appears to form long, narrow, wedge-shaped masses a few 
hundred yards wide. 
The rock presents characters similar to those of the last-described 
type, but it is typically rather finer grained, and its felspar content 
(labradorite-bytownite) ranges from 10 to 20 per cent. Its specific gravity 
is slightly lower (3'22). The felspar is interstitial to the enstatite crystals, 
and contiguous particles of the formal mineral may be in optical con- 
tinuity over a centimetre or more. 
The accessory minerals of the felspathic enstatitites are as follows : 
Monoclinic pyroxenes, micropegmatitic quartz and felspar, red-brown 
mica, pale green mica, pyrite, chromite, bastite, and chlorite ; all these 
occur in minute quantities only. The same minerals are present in the 
felspathic websterite. 
By increase of the pale green monoclinic pyroxene, which is a fairly 
constant accessory, the rock passes into an interesting variety approaching 
w^ebsterite. This may be called felspathic websterite or pyroxene-rich norite 
(Plate III, fig. 6). Such a rock exposed for a width of about 150 feet in the 
foothills of the Selundi range, a mile or so north of Secombi's Kraal and 
in a similar position north-east of the Invulnerable Mine, is exactly like 
the felspathic enstatitite excepting for the large diopside diallage crystals 
developed in it These have very irregular outlines, but tend to be idio- 
morphic ; they stand out prominently from the finer grained enstatite- 
felspar-matrix on weathered surfaces, and are up to 3 centimetres in size. 
The two pyroxenes would appear to be in about equal proportions, whilst 
a third pyroxene (a monoclinic variety) is also present. The felspar 
(bytownite-anorthite) occupies from 10 to 15 per cent, of the volume of 
the rock, and encloses the fine-grained idiomorphic pyroxenes poiki- 
litically. 
Tlie Peridotites and Picrites. — Like the felspathic enstatitite, the 
peridotites (Plate IV, fig. 1) appear to be confined to long, narrow, 
wedge-shaped masses, which die out in the pyroxenites to mere strings 
and veins. They afford outcrops from 50 to 100 yards wide, but in places 
the width may considerably exceed this, whilst they may be up to a couple 
of miles long. Usually the rock is only seen in the beds and banks of the 
XJmtebekwe and Little Tebekwe rivers, where it weathers spheroidally, 
but it outcrops in the large vlei between the two arms of the Selundi 
range on Unki farm and again in the gap in the Selundi range on 
Edward's farm, through which the Victoria road passes. These poorly 
resistant olivine rocks thus outcrop in the low ground only. They 
are exposed in the following places : Near the junction of the Little 
