CHEMICAL COMPOSITION OF GRANITE AND NODULES. 169 
line, thus far found, occurs as a bunch of grains irregular in shape, dark 
in color, and with strongly marked pleochroism in pale gray and dark 
eray-blue tints. It is uniaxial and negative, and is associated with 
quartz and feldspar, and in one or two cases was seen to be penetrated by 
a few sillimanite needles. 
CHEMICAL COMPOSITION OF THE GRANITE AND OF THE NODULES 
In order to make a comparative study of the chemical composition 
of the granite and the nodules, a specimen was selected consisting of the 
typical granite in which there was enclosed a nodule spherical in shape 
and two inches in diameter. The specimen was broken up and the gran- 
ite, excepting that immediately surrounding the nodule, was crushed and 
anaverage sample of it drawn. The nodule, after having been very care- 
fully freed from the adhering granite, was broken across and one-half 
taken for analysis. The analyses were in each case carried out in dupli- 
cate, the figures given below representing the mean of two closely con- 
cordant determinations :* 
Granite. Nodule. 
Sillicalneeennnior aaa Lista 78.83 81.43 
PAIN heyeare Reac nro cioaye« os 10.88 13.70 
IRSPEC Cx, ,cbovoseoeoepeae 1.63 1.58 
ILA TIGS Aesocys doo eee en eee 52} Bovih 
Miaiomesianeeererinecias a RR aAS .30 06 
JEXOLENSI OY Sensis hoe Meeereeeerene eS D.oL 1.28 
Sod armen preg ut sec). iis fake BAB 1.02 
LOSS CM WAMUNON, soo sden05 500 On -92 
99.67 100.36 
Boracic acid was not looked for. The silica in a second nodule was 
found to amount to 79.19 per cent. 
The analyses bring out the fact that the granite is a very acid one, and 
that the chief difference between it and the nodules is that the latter are 
richer in silica and alumina and poorer in alkalies than the granite 
itself. Among the minor differences is the marked preponderance of 
potash over soda and, owing to the presence of the biotite, the larger 
percentage of magnesia, in the case of the granite. 
A study of thin-sections of this particular specimen of granite showed 
it to be composed chiefly of quartz and microcline, with a small amount 
of biotite, plagioclase, and an untwinning feldspar, probably orthoclase. 
Very small amounts of muscovite and iron ore were also present. 
The exact composition of the several minerals present not being known, 
it is impossible to calculate the percentages in which they are found in 
* They were carried out in the laboratories of McGill University by Mr Nevil Norton Evans. 
