340 The American Geologist. June, i904. 
biotite, and magnetite, with numerous patches of calcite from 
the weathered feldspars. 
Plagioclase feldspar is the dominant mineral in the section ; 
it is idiomorphic and shows polysynthetic twinning after the 
albite law. From a number of measurements taken upon the 
twinning face, the extinction angle of one set of crystals has an 
average of 5° indicating oligoclase, while measurements taken 
on the twinning face of another set of crystals vary from 21° 
to 28° indicating labradorite. 
Oligoclase is more abundant than the labradorite ; the crys- 
tals have a maximum size of .5 mm. in length and .2 mm. in 
width. The plagioclase shows alteration in some cases to cal- 
cite. A few crystals of quartz and orthoclase were noted. 
Biotite is seen surrounding the feldspar crystals and is 
weathered in many cases to green chlorite. Calcite and epidote 
occur in irregular aggregates from alteration of the feldspars. 
There is a small amount of augite in the rock somewhat al- 
tered to hornblende, and showing a maximum length of .7 mm. 
and a maximum width of .4 mm. 
Minette. — The rock referred, to under this class of lampro- 
phyres (19 Rossland) occurs as a 20 foot dike at the 900 foot 
level in the Josie and Le Roi mines, and is a medium grained 
rock, of a dark gray color, with crystals of biotite and green- 
ish white fibres of natrolite. These minerals are imbedded in 
a grayish groundmass which upon microscopical examination 
proves to be chiefly feldspar, the orthoclase being dominant 
over the plagioclase. 
In a thin section, Fig. 7, the rock is porphyritic with pheno- 
crysts of biotite in considerable quantities, and a smaller amount 
of monoclinic pyroxene. The ground mass is composed large- 
ly of orthoclase and plagioclase ; the orthoclase is greatly in 
excess of the plagioclase. 
The biotite is idiomorphic and occurs in large phenocrysts ; 
it is very pleochroic, changing from dark reddish brown to light 
brown ; the crystals reach a maximum length of .75 mm. 
The monoclinic pyroxene is diopside ; it has a pale greenish 
color with slight pleochroism and occurs chiefly in long pheno- 
crysts; it has a maximum length of .'5 mm. and a maximum 
width of .1 mm. 
