6 
Transactions of the Boyal Society of South Africa. 
and on the other nothing but pyroxenite. And in the hilly ground on 
Adare farm pyroxenite (which forms the edge of the intrusion and is 
seen in the river-bed) occurs high up in the hills and at an appreciably 
greater height than the lowest of the norite exposures a quarter of a mile 
away opposite the hills. Again it must be remembered that this deeply 
dissected hilly ground in the schists alongside the intrusion nowhere was 
found to expose Great Dyke rocks such as would be the case if the 
intrusion were a gently dipping sheet. Neither is there any evidence 
of a fault along the western edge subsequent to the intrusion. 
In the Selukwe section the arrangement of the variations is bilaterally 
symmetrical, the least basic rock lying in the middle (excepting the granite 
veins and bosses which are confined to the marginal basic portions). 
Close examination shows this differentiation to be quite sharp. 
The regular arrangement does not, however, always hold good. The 
long central mass of felspar-rich norite gives place here and there (where 
the surface level becomes low) to the more basic types which then occupy 
the whole width of the intrusion. Very occasionally also the felspar-rich 
norite occurs in isolated, irregular, rounded outcrops, perhaps as small 
bosses. This latter habit may indeed be extended to the whole of the 
centrally placed norite ; that is, it may be one of a series of very much 
elongated bosses. 
Perhaps the chief difificulty encountered in the Selukwe area against 
regarding the intrusion to be a dyke is that, as in the Belingwe portion 
described by Wagner, there are in several places exposures which show 
bedded structure and interbedded arrangement of the different rock types. 
Thus : (1) Below the Victoria road drift in the Umtebekwe a small cliff 
in the river bank exposes peridotite with pyroxenite beneath, the rocks 
having a small easterly dip. The exposure suggests a series of parallel 
sheets. (2) A mile north of the Victoria road drift in the Little Tebekwe 
a bed of serpentine several feet thick, lying in enstatitite, similarly has an 
easterly dip. (3) The chromite seams on Good Hope dip at small angles 
(12°-25°) ? eastwards. (4) It is commonly to be noted in small exposures 
that the rocks have a sort of bedded or horizontally jointed structure. 
Further, the Selundi range where broad has the appearance of a general 
gentle slope to the north-west. It is to be noted here also that the small 
boss-like bodies of websterite breaking abruptly through the pyroxenite 
commonly weather with a horizontal stratiform structure, as also do the 
rounded bodies of granitic rock. 
It is not inconceivable perhaps that this bedded arrangement of the 
peridotite and pyroxenite might be formed here and there during the slow 
cooling of a fluid magma of a dyke undergoing differentiation in place. 
Such might be produced by the progressive differentiation of that 
portion of the magma parent of the two rock types and the action of 
