CUPRIFEROUS PORPHYRITE AND QUARTZ VEINS. 57 
On closer examination I found that wherever the copper 
contents were at all noticeable the lava also contained 
numerous inclusions of crystallised limestone, schist, slate, 
quartz and rhyolite. Where the basaltic rock was free 
from these inclusions the copper ores were also absent. 
On my return to Sydney I assayed a sample of the basalt 
free from inclusions to see if copper was an essential con- 
stituent of it. I powdered carefully about 10 tbs. of the 
basalt and took 10 grams of the powder to test. Not the 
faintest trace of copper was indicated. 
It appears from these considerations that the copper 
here is not an original constituent of the igneous magma, 
as it is in the cupriferous andesites and: tufis of the Illa- 
warra district. It is undoubtedly derived from a metal- 
liferous lode through which the basalt has burst, though 
the small masses of dendritic native copper and mossy 
malachite, obtained in the weathered portions of the mass, 
are formed by the secondary alteration of the original 
inclusions of sulphide and oxide ores. 
The basaltic mass which I examined in a valley near 
Sugarloaf Mountain is over half a mile wide and extends 
in a north and south direction for about ten miles, and 
patches rich in copper inclusions occur here and there, I 
am told, along its whole length. It is therefore probable 
that this lava has found its way to the surface along a 
fissure vein containing rich metallic ores. The copper ores 
obtained in the basalt contain gold. From an economic 
point of view the occurrence is valueless, the basalt being 
nowhere rich enough in metal to pay for the extraction. 
It may however be possible to pick up the ore-body to the 
north or south of the basaltic intrusion. 
The rock here termed basalt is a volcanic rock, in places 
quite vesicular and amygdaloidal. Its petrological descrip- 
tion is appended.* Basalt is an appropriate field name. 
