Igneous Rocks of KossUmd. — B. C . Barber . 343 
dark to light brown. Tlic crystals have an average width of 
.3 mm. in cross section. 
The monoclinic pyroxene present is idiomorphic, and con- 
tains inclusions of feldspar; it is diopside and is changed around 
the borders to hornblende ; the maximum size of the crystals is 
I cm. in length and i mm. in width. 
Basic Monaonyte. — The monzonyte (53 Rossland ) herein 
described as a medium-grained, gray, massive rock occurring at 
the 300 foot level of Le Roi No. i mine ; it is rather fine-grained 
with phenocrysts of amphibole, pyrite, and biotite, which may 
be detected with the naked eye. 
In thin sections the rock is seen to be holocrystallinc, and 
composed largely of feldspar and hornblende. The hornblende 
is hypidiomorphic, with characteristic cleavage and with pleo- 
chroism from brown to green ; the maximum length of the 
crystals is .5 mm. and the maximum width is .2 mm. 
The plagioclase feldspar occurs in lath-shaped crystals, is 
invariably twinned, and shows the idiomorphic character quite 
distinctly ; it is chiefly oligoclase, as showrf by its having very 
small extinction angles on the albite twins. It is somewhat kao- 
linized and contains inclusions of hornblende. 
The small amount of biotite present shows crushing. Or- 
thoclase and magnetite are also present in small quantities. 
Syenyte-Monzonyte. — The country rock (27 Rossland) of 
the Le Roi mine is not a true syenyte, but approaches a mon- 
zonyte. It is fine grained and of a light gray color. 
In thin sections. Fig. 9, the rock is holocrystallinc, is gran- 
ular and more acid than the monzonyte from the Iron Mask 
mine. The amphibole is idiomorphic, with the strong pleochro- 
ism, changing from almost colorless with a slight greenish tint 
to a deep green color; its maximum length is i. 4 mm. and the 
maximum width is .35 mm. Orthoclase is noted in small ir- 
regular shaped crystals which are frequently twinned according 
to the Carlsbad law ; the maximum length is .4 mm. and the 
maximum width is .15 mm. 
The plagioclase is idiomorphic and considerably weathered 
to calcite ; the crystals show polysynthetic twinning, and a num- 
ber of readings of the extinction angle on the twinning face 
varied from o" to 5^ indicating the presence of the soda-lime 
feldspar, oligoclase; their maximum length is 1.7 mm. and 
their width is 4.5 mm. 
