14 Transactions of the Boyal Society of South Africa. 
latter mineral also forms interlamellar growths with the enstatite. 
Chromite is characteristically associated with the browm mica, and 
occurs in small rounded or perfect crystals ; it is abundant in places, and 
tends to segregate into patches and well-defined thin seams seldom more 
than 6 or 8 inches thick, from which the olivine and the enstatite are 
partially or totally excluded. These seams are further described below. 
An interesting variety of harzburgite occurring in the Little Tebekwe 
river west of Marishengwa may be mentioned here. It consists of large 
(I'O centimetres), closely set poikilitic enstatites lying in an olivine- 
chromite base, the two minerals being in almost equal proportions. The 
olivine is medium-grained (1-2 millimetres), granular and free from 
chromite inclusions ; whilst the chromite forms a finely (0-25-0-5 milli- 
raetre) crystallized interstitial aggregate. The enstatite individuals have 
included chromite, olivine, and brown mica. 
Locally the peridotites are much serpentinized, but even then the 
enstatite present has remained almost unaltered. These serpentines are 
w^ell represented east of the Victoria road drift across the Umtebekwe 
river. 
By increase of monoclinic pyroxene and felspar at the expense of 
olivine the peridotite in several places grades insensibly into picrite. 
This may contain up to 20 per cent, of felspar, although usually the 
proportion appears to be considerably less. The rhombic pyroxene has 
largely given place to a monoclinic species. 
The picrite does not occur without peridotite. The former is merely 
a facies of the latter or vice versa, and is apparently of much more limited 
occurrence. The picrites are coarse-grained rocks, in appearance closely 
resembling the peridotites, but always showing their felspar conspicuously, 
giving the rock a speckled appearance, whilst they are less commonly 
poikilitic than the peridotites, chiefly by reason of the failure of enstatite 
to assume a prominent proportion. The mica, however, and, in some 
specimens, the felspar show poikilitic structures. 
A typical specimen with sp. gr. 3-01 was found to consist essentially of 
olivine, diopside diallage, basic felspar (about 20 per cent.), and red-brown 
mica in decreasing order of abundance, with small quantities of enstatite, 
chromite, and magnetite. 
The Wehsterites (Plate IV, figs. 2 and 3). — This rock type is limited to 
small boss-like bodies from a few yards in diameter to perhaps 150 feet. 
They lie entirely in the basic margins of the intrusion and chiefly in the 
enstatitite, but also in the coarse-grained websterite near Secombi's Kraal, 
and in the felspathic enstatitite. It is probable that the rock represents a 
differentiation product of the hypothetical enstatite picrite partial magma, 
the opposite differentiation being Iherzohte, which is, however, scarcely 
represented in that part of the intrusion examined. 
