8 
Ti^ansactions of the Boyal Society of South Africa. 
(largely non-aluminous), still less mica and very little iron ore, traces of 
soda-lime felspars and quartz. Enstatite is ubiquitous, so also are 
bytownite, diopside, and pyrites, but less prominently, the last named 
being in very small amount. 
The rocks are divisible chiefly into two well-marked types, namely 
felspar-rich norite and enstatitite. A subordinate type intermediate between 
these two exists in felspathic enstatitite, which contains from 10-15 per 
cent, of felspar, whilst a fourth type, also subordinate and the most basic 
of the intrusion, is enstatite-peridotite. 
A fifth type occurring in isolated bosses of small extent is a pyroxenite 
composed of orthorhombic and monoclinic pyroxenes and agreeing with 
the American websterites, whilst a sixth type also strictly subordinate to 
the main types and occurring in veins and bosses, is a peculiar granite 
representing a very acid phase of the magma ; it is associated in some 
instances with norite-pegmatite. 
Quartz veinlets and chromite seams are respectively the most acid and 
basic modifications of the intrusion, whilst norite, picrite, Iherzolite, 
olivine gabbro, and felspar-rich gabbro are local variations of one or 
other of the above-mentioned types. 
Enstatite-bearing olivine serpentine and bastite-rock are respectively 
altered forms of the peridotites and enstatitites. 
The rocks of the Great Dyke in the area examined may therefore be 
grouped as follows in decreasing order of extent : — 
^ ,( Felspar-rich norite ] Dominant types in very laree 
Roughly equal „ f ^.^.^ ^ J ^ 
^ ^ (Ijnstatitite j amount. 
Ditto 
{Felspathic enstatitite... j Subordinate types in fair quan- 
Enstatite-peridotite ...J tity. 
Granite | Subordinate residual types in veins 
Websterite ) and bosses in small quantity, v 
Picrite 
Norite 
Lherzolite 
Olivine gabbro 
, . , 1 ^ \ Variational and residual types m 
Feispar-ricn websterite). ^ 
, . , , 1 / very small amount. 
Felspar-rich gabbro 
Norite pegmatite ... 
Quartz-felspar veins ... 
Chromite-olivine seams/ 
Enstatite-beariner olivine serpentines ...^ . ,^ -, , 
^ . , ^ ^ ^Altered rocks. 
i3astite-rock J 
Felspar-rich Norite (see Plate III, figs. 1-3). — This rock constitutes 
the central part of the intrusion and solely forms the long Selundi range, a 
