264 J. MILNE CURRAN, 
alkalis ene carefully searched for but were found not to be 
present. 
Basaltie Rock.—In the estimation of the alkalis, the double 
chlorides of sodium and potassium were weighed, then the Cl deter- 
mined volumetrically. The proportion of Na and K was then 
calculated by the formula given in Thorpe. The K was also 
specially determined by the PtCl, method. 
I am indebted to the following works in studying gems and 
precious stones :— 
“Minerals of New South Wales.”—Liversidge. 
“Gems and Precious Stones.”—Kunz. 
“Precious Stones and Gems.”—Streeter. 
“Precious Stones.”—Church. 
“System of Mineralogy.”—-Dana 
“The Science of Gems.’ dis Abbott 
“Select Methods of Chemical Analysis. ee 
“Mineral Analyses.” W ohner. 
“Encyclopédie Chimique.”—Fremy. 
* CONCLUSION. 
Diamond—New South Wales diamonds are characterised by 
(a) ahigh specific gravity ; (b) a superior hardness and a fine 
lustre ; (c) an absence of pronounced cleavage. Although some 
stones five to eight carats have been found, the bulk of the stones 
are small, three to the carat. The diamond is widely distributed 
but is found in three localities only, in quantities sufficient to be 
considered economically important :—Bingara ; Inverell district, 
including Cope’s Creek, Round Mount, and Staggy Creek ; and 
Two-Mile Flat, near Mudgee. The original matrix of the diamond — 
has not yet been discovered. The diamonds hitherto found occur 
in drift, and there is no evidence to show they were formed in 
these drifts. The probability is that the diamond is derived 
from a matrix occurring higher up the Dividing Range than any 
diamond bearing wash known at present. 
Sapphire—Sapphires are found chiefly in the tin-bearing drifts 
of Tertiary and Post-Tertiary age of the Emmaville and Tingh® — 
