Igneous Rocks of Rossland. — B. C. Barber. 345 
The hornblende is idiomorphic and has two generations of 
crystals ; those of the first generation have a maximum length 
of imm. and a maximum width of .3mm., and are strongly plen- 
chroic, changing from green to brownish ; those of the second 
generation have an average length of .2 mm. and an average 
width of .1 mm. 
Pyrite, biotite, quartz and magnetite are present in small 
quantities. 
Hornblende Dioryte. — A part of the country rock on the 
footwall side of the ore vein at the 900 foot level in the Le Roi 
mine is a hard, coarse grained, light colored dioryte (3 Ross- 
land). It has a granular, holocrystalline structure with large 
crystals of amphibole and biotite which can be easily detected 
with the naked eye. A microscopical examination of the rock 
shows the white mass to be feldspar, many of the crystals show- 
ing their true form. 
A thin section of this rock shows the predominant mineral 
to be idiomorphic hornblende occurring in crystals having a 
maximum length of 1.7 mm., and a maximum width of i mm. ; 
some of this is secondary (uralite) being altered from augite. 
Plagioclase occurs in lath-shaped crystals, polysynthetically 
twinned after the albite law, containing numerous inclusions ; 
they have a maximum length of 2 mm., and a maximum width 
of .7 mm.; the extinction is almost parallel, indicating oligo- 
clase. Some orthoclase crystals were seen, as well as small 
crystals of quartz . Biotite was noted occurring in irregular 
shaped crystals, partly altered to chlorite. Epidote and mag- 
netite are also present. 
Dioryte Porphyry. — A large stock of this porphyry (13 
Rossland) occurs as the country rock common to all the mines 
of the Rossland district. It is of a dark color with large phen- 
ocrysts of monoclinic pyroxene, biotite, amphibole, and feld- 
spar, in a .finely crystallized groundmass, which, under the 
microscope, proved to be hornblende, feldspar, and biotite. 
In thin sections, Figs, ii and 12, the feldspars are seen to be 
plagioclase ; they are idiomorphic and are polysynthetically 
twinned, after the albite law ; the crystals have a maximum 
length of 1.2 mm. and a width of .4 nmi. ; a number of readings 
of the extinction angles on the twinning planes varied from 
21" to 28° indicating labradorite. 
