GABBROS OF EAST SOOKE AND ROCKY POINT. 
15 
much as 60 per cent of the total mass, ancUproportions of 35 to 
40 per cent are common. Very sodic feldspar, about Ab S5 An 16 , 
often graphically intergrown with the quartz, is the other prin- 
cipal component; and the ferromagnesian elements are repre- 
sented by a few shreds, rarely amounting to more than 2 or 3 
per cent, of hornblende, chlorite, or mica. A little titanite is 
commonly present. The quartz is usually concentrated towards 
the centre of the veins, and occasionally the centre of a vein or 
apophysis is composed almost wholly of it. 
Aplite replacements generally take the form of rounded 
apophyses rather than veins. They are not nearly so numerous 
as the aplite veins or the hornblendite replacements, but numer- 
ous enough to show that the aplitic solutions attack and alter 
the gabbro when forced into intimate contact with it. The ten- 
dency of the alteration is to convert the gabbro into aplite of the 
vein type. Under the microscope the augite of the gabbro is 
seen to have been changed to hornblende and biotite, calcic 
feldspar to more sodic, and ilmenite to titanite and magnetite; 
and quartz has been deposited in intermineral spaces. 
The aplites are younger than all the rocks previously 
described, as they cut them all indifferently. They are probably 
older than the copper ores and the faulting which preceded the 
deposition of the latter. The evidence on these points is, how- 
ever, largely inferential and may be summarized as follows : 
No copper ores or oj*e minerals of any kind, with the excep- 
tion of occasional grains of magnetite, have been found in any 
aplite vein. 
Aplites are everywhere found cutting the hornblendite 
veins, except the large hornblendite zones which were faulted 
before ore deposition took place. Whitish fragments of sodic 
feldspar are fairly common in these big zones. The probability 
seems strong that the aplite veinlets must once have cut them 
also, but were destroyed by the later faulting, and that the feld- 
spar fragments are all that now remain. 
Ore veins are generally a later product of differentiation 
than igneous veins. 
