Great Dyke of Norite of Southern Bhodesia. 
17 
granite. The rocks of the different bodies vary considerably, a felspar 
quartz biotite rock is perhaps the commonest ; other types devoid of 
ferromagnesian minerals are strictly aplites and pegmatites, and even 
pegmatite quartz-veins when they consist entirely of quartz ; still another 
type which may be called norite-pegmatite consists of very coarse 
aggregates of bastite and felspar. 
The injections generally have their length parallel, or nearly parallel, 
to the margins of the Great Dyke, but they may take any direction, for 
instance, in the centre of Edward's farm alongside the Victoria road 
granite veins have intruded at right angles to the length of the Great 
Dyke. 
These veins and lenticles appear to be the latest phase — a residual 
leucocratic differentiation of the Great Dyke magma. They intrude 
into the pyroxenites and peridotites, but are generally in the former. 
Although in places the veins strike almost at right augles to the felspar- 
rich norite, they are never traceable into that portion of the Great Dyke. 
And although distributed throughout the basic parts of the Great Dyke 
these curious granite bodies tend to be distributed in groups over a 
small area. 
During the preliminary examination of the district it was thought that 
the granite veins in the Great Dyke might be the representatives of a 
granite later in date than the Great Dyke, rather than leucocratic 
modifications of the norite, but subsequent detailed work has led to the 
conclusion that this is not so, but that they belong to the Great Dyke 
itself, i.e. are part of its magma. The facts which lead to that conclusion 
are as follows : — 
1. Although the veins are numerous and generally very close to and 
even at the edge of the intrusion, and although in places they strike 
straight at its edge, they are never traceable into the granite and other 
rocks into which the Great Dyke has intruded. This fact and the con- 
clusion drawn therefrom are borne out by Wagner (loc. cit., p. 51) in the 
Belingwe section of the Great Dyke. 
2. The rocks of the veins, although varying considerably in texture and 
mineralogical composition, do not resemble any of the pegmatite, aplite, 
or felsite veins of the Granite, but are mostly characteristically different. 
3. The bastite-felspar rocks (norite pegmatite) are found to be part of 
and to grade into the granibe veins in the Great Dyke. 
4. The veins are generally parallel to the trend of the intrusion as are 
the other component parts of the latter. 
The veins vary from an inch or so to 10 or 12 feet Vvide, and average 
3 feet. Their length is very variable ; generally they are quite short — 
50 feet or so — but some are more than half a mile long. They usually 
pursue a perfectly straight course, but in some instances suddenly bend at 
2 
