342 The- American Geologist. June, 1904. 
The monoclinic pyroxene is diopside; it occurs almost en- 
tirely as phenocrysts, though in not nearly such great abund- 
ance as the hornblende ; it is light green with faint pleochroism ; 
the larger crystals are somewhat altered, while the smaller ones 
are quite fresh. 
The ground mass of this rock is made up almost entirely 
of anhedrons of feldspar interwoven around the pyroxene and 
hornblende, with crystals of magnetite and apatite filling the 
inter-spaces. Orthoclase is much more abundant than the plag- 
ioclase ; it averages .05 mm. in diameter. The plagioclase is 
banded and a number of readings of the extinction angle on 
the twinning faces gives an average of S°* indicating oligoclase. 
Apatite is present in the ground mass in numerous clear, 
colorless needles. 
The country rock (102 Rossland) at the 700 foot level of 
the War Eagle mine is a vogesyte. Fig. 8. It closely resembles 
the preceding rock, but has in addition large phenocrysts of 
plagioclase feldspar. The feldspar in the groundmass is almost 
entirely orthoclase. 
GRANULAR ROCKS. 
Monsonyte. — This augite syenyte, or monzonyte, (59 Ross- 
land) is a massive rock found in the Iron Alask mine, and it is 
a coarse grained, light colored rock showing feldspar, biotite, 
augite, and hornblende to the naked eye. It is intermediate be- 
tween syenyte and dioryte. 
In thin section the rock is granular with large crystals of 
feldspar and augite, having a maximum length of i cm. Orth- 
oclase is abundant ; it has a maximum length of 2 mm. and a 
maximum width of i mm. ; it is idiomorphic and twins after the 
Carlsbad law, the twinning boundary being bent or jagged. 
Inclusions of plagioclase are common ; these have an average 
length of .4 mm. and a width of .3 mm. 
There is much plagioclase present in long lath-shaped crys- 
tals; these are smaller than the orthoclase, are idiomorphic, 
show polysynthetic twinning, and some show zonal structure. 
A number of readings of the extinction angle on the twinning 
face ranged from 1° to 5°, indicating oligoclase. The crystals 
have a maximum length of .5 mm. and a width of .2 mm. 
Small quantities of biotite with some inclusions of feldspar 
are noted ; it is idiomorphic and has a distinct pleochroism from 
