Great Dyke of Norite of Southern Bhodesia. 
13 
Tebekwe and the Lundi rivers and northwards on Lubonga, Good Hope 
and Mount Bougai farms, in the Chibi road drift across the Little Tebekwe 
river, south of the Selundi road drift across the same river, east of the 
Little Tebekwe river near the boundary of Paarl and Pink Un farms, in 
the Umtebekwe near the north-east beacon of Selukwe Peak, and on 
Depoto and the northern part of Uncima farms. The peridotites are 
never in contact with the felspar-rich norite, but have pyroxenites on both 
sides. In one or two places they may form the actual margin of the Great 
Dyke, e.g. on Paarl and Depoto farms ; but this is doubtful. They are 
thus regarded as direct separations from the second rock magma alluded 
to below (the hypothetical enstatite picrite), and indeed the picrites of the 
Great Dyke, which are here only found grading into the peridotites, may 
perhaps be regarded as residual parts of the hypothetical magma which 
thereby would become no longer hypothetical. 
The peridotites are largely typical harzburgites (saxonite or enstatite- 
peridotite). The enstatite-peridotite serpentine from the Marico district 
(Vaalkop), described by H. Kynaston (loc. cit., p. 58), is similar in all 
respects to many of those of the Great Dyke. They are rather coarse- 
grained, dark brown or greenish to nearly black rocks, consisting essen- 
tially of olivine and enstatite in roughly equal proportions, although, in 
many instances, the olivine is in excess of the pyroxene, and rarely may 
be almost the sole constituent, when the rock becomes a dunite ; whilst in 
other instances the enstatite is largely in excess of the olivine, when the 
rock may be called an olivine-bearing enstatitite. 
The olivine forms granular, equidimensional, rounded hypidomorphic 
grains (Plate IV, fig. 1), which in thin section are nearly colourless and 
usually remarkably fresh. Whether fresh or serpentinized they contain a 
very small amount of iron ore (magnetite). The enstatite is characteristic- 
ally poikilitic, i.e. interstitial to the olivine, and forms large rounded 
individual patches, optically continuous over 3 or 4 centimetres, 
thereby imparting the characteristic lustre-mottling to the rock ; the 
porphyritic nature is more complete in some specimens than in others, 
i.e. there are fewer inclusions of olivine. In some rocks these large 
poikilitic enstatites are so close together that a relatively small amount of 
olivine ground-mass exists. The name " harzburgite porphyry," used by 
Wagner (loc. cit., p. 51), is an apt one for these rocks. The enstatite is 
pale green to dark brownish in the hand specimens, but in thin section is 
nearly colourless. Dark red-brown mica is a constant accessory, it also 
encloses the olivine poikilitically. Chromite, felspar, monoclinic pyroxene, 
and magnetite are the other accessories ; whilst serpentine, bastite, 
chlorite, and magnesite are alteration products. The felspar is much 
altered, and together with the monoclinic pyroxene (pale green diallage), 
occurs interstitially in very small and irregularly distributed particles ; the 
