Great Dijke of Norite. of Southern BJiodesia. 
15 
Some ten or twelve of these small masses were observed, chiefly in the 
Umtebekwe valley, where they are well represented at the foot of the 
Selundi range north of Secombi's Kraal, on Depoto farm, and on 
Makomisa farm. 
In all these places the websterite forms small rocky hillocks 12 feet 
or less high, but up to 60 -70 feet ; some of them weather with stratiform 
appearances. 
x\s might be expected from their mode of occurrence, the websterites 
exhibit considerable differences mineralogically, but texturally they are all 
alike, namely, very fine-grained and saccharoidal. The grains are nearly 
equidimensional in general, but occasionally small patches or streaks 
of coarser grain are present. Their colour is dark grey to sage-green. 
The structure (especially of those which contain a fair amount of felspar) 
■ — the norite and gabbro (Plate IV, figs. 4 and 5) — closely resembles that 
of the Saxon " granulites." Their specific gravity is high (3"24:-3'28). 
In the typical websterite (Plate IV, fig. 2) enstatite and diopside 
are the essential constituents and are in about equal proportions, the 
rhombic pyroxene rather exceeding the monoclinic species. Both minerals 
are nearly colourless in thin section, and form a mosaic of irregular rounded 
indented granules. The minutest quantity of interstitial plagioclase is the 
only other constituent. 
Varieties containing other minerals approach Iherzolite (when acces- 
sory olivine is present), (Plate IV, fig. 3), norite or felspathic enstatitite 
(when diopside is lacking), (Plate IV, fig. 4), or olivine-enstatite gabbro 
(when olivine and plagioclase are largely present and rhombic pyroxene is 
an accessory in very small amount), (Plate IV, figs. 5 and 6). This last- 
named rock is an interesting one. It forms a small outcrop on the east 
bank of the Umtebekwe river near the Victoria road. It lies in enstatitite 
and serpentine, and is a fine-grained granular dark grey rock with specific 
gravity 3'10, and composed of the following minerals in decreasing order 
of abundance, finely granular labradorite-bytownite usually untwinned ; 
pale grey-green, slightly pleochroic diopside diallage, allotriomorphic and 
poikilitic ; colourless olivine containing rather much fine dusty magnetite 
and minute round inclusions of felspar; pleochroic enstatite in irregular 
growths partly or completely surrounding the monoclinic pyroxene and in 
places joining up six or eight diopside and olivine grains into a small 
cluster. The micro-photograph (Plate IV, fig. 6) is taken in such a 
position between crossed nicols as to show the narrow rims of rhombic 
pyroxene surrounding extinguished grains of monoclinic pyroxene. 
The Chromite Seams. — These were found only in one place, namely, 
in the centre of Good Hope farm, about half a mile west of the Little 
Tebekwe river. An unusually wide stretch of harzburgite occupies the 
greater part of the flat and gently rising ground from the river to the foot 
