3zH ^^'^ American Geologist. J^^e, 1904. 
Biotite is noted in small quantities. A small amount of 
quartz is also present ; the crystals are clear, irregular in shape, 
have a low relief, with low interference colors and no cleavage. 
The section also shows a small amount of augite, that has been 
altered to hornblende, and some magnetite. 
Syenyte Dike. — On the 200 foot level of the Le Roi No. i 
mine is a dike of syenyte (55 Rossland) about ten feet wide; 
it is a light gray rock with small phenocrysts of hornblende in 
a ground mass which proves to be feldspar under the micro- 
scope. 
In thin sections the hornblende is hypidiomorphic, with a 
maximum length of .4 mm. and a maximum width of .1 mm. 
It is strongly pleochroic, changing in color from dark to brown- 
ish green and shows no zonal structure. 
M'onoclinic pyroxene (diopside) is seen in small crystals 
showing the results of crushing; their average length is .25mm. 
and an average width is .07 mm. ; it has a high relief and in- 
terference colors higher than those of the hornblende. 
The groundmass of the syenyte is made up of feldspar ; 
this is very largely orthoclase, some showing twinning accord- 
ing to the Carlsbad law; the plagioclase crystals have almost 
parallel extinction, indicating oligoclase. 
Quartz is present in small quantities as anhedrons. Grains 
of magnetite and pyrite are also present. 
Syeiiyte Porphyry. — This porphyritic rock (57 Rossland) 
is finer grained than the monzonyte of the Iron ^lask mine, 
and occurs as a 60-foot dike in the Le Roi No. i mine. It is 
light colored, and shows phenocrysts of biotite. hornblende, 
and feldspar in a whitish groundmass which proves under the 
microscope to be feldspar. 
In a thin section, Fig. 10, the rock is panidiomorphic, with 
a few large crystals of feldspar, biotite, and hornblende in a 
groundmass composed of fine crystals of biotite, feldspar and 
augite. 
Orthoclase and plagioclase are almost evenly divided in 
numbers ; orthoclase shows alteration to kaolin, while the plag- 
ioclase is somewhat changed to kaolin and calcite; the plagio- 
clase is oligoclase and shows polysynthetic twinning ; the aver- 
age size of these crystals is about 4 mm. in length and about 
1.7 mm. in width. 
