Igneous Rocks of Rossland . — B. C. Barber. 341 
The feldspars occur in tlie ,£(round mass; orthoclase is ir- 
regular in shape and twinned after the Carlsbad law. A num- 
ber of readings of the extinction angle on the twinning face 
of the plagioclase crystals varied from 0° to 5° indicating the 
acid soda plagioclase, oligoclase ; these have distinct cleavage, 
show polysynthetic twinning after the albite law, and have a 
maximum length of .35 mm. 
Amphibole (hornblende) occurs in the ground mass as an 
alteration from diopside (uralite). A small quantity of chlor- 
ite is shown in the section, due to weathering of the biotite. 
Calcite occurs as a weathering product from plagioclase. Mag- 
netite ^nd pyrite are distributed abundantly in small crystals. 
Apatite occurs in the form of elongated or needle-like crystals, 
widely distributed throughout the ground mass. 
Aggregates of colorless crystal fibres, somewhat kaolinized 
and possessing a spherulitic structure are noted. These crys- 
tals, which are probably natrolite, are weakly doubly refract- 
ing having an interference color about yellow, of the first order, 
in rather thick slides, and occurs as an alternation product of 
plagioclase. 
Vogesyte. — In a railroad cut near the workings of the Le 
Roi mine, is a medium grained rock (18 Rossland) with a gray 
color, showing large phenocrysts of monoclirlic pyroxene and 
amphibole which have a maximum length of 1.25 mm., and can 
be detected readily with the naked eye; the ferro-magnesium 
minerals lie in a groundmass of feldspar. 
In thin section this rock is seen to be a lamprophyre with 
phenocrysts of pyroxene and of hornblende, the hornblende be- 
ing in greater abundance than the pyroxene. The spaces be- 
tween the ferro-magnesium minerals are filled with alkali feld- 
spars in excess over plagioclase, apatite, magnetite, and pyrite. 
The amphibole is idiomorphic, occurring almost entirely as 
phenocrysts; it is of the basaltic (brown) _ hornblende type, is 
chiefiy primary, and has a maximum size of 1.25 mm. in length 
and .4 mm. in width. In sections parallel to the C axis, the 
hornblende shows parallel cleavage, and strong absorption par- 
allel to the direction of elongation and cleavage. The crystals 
show frequent twinning, and exhibit strong pleochroism from 
dark to light brown ; some of the hornblende is secondary, be- 
ing derived from alteration of the pyroxenes. 
