336 The American Geologist. June, 1904. 
direction and were immediately filled by intrusive dikes. There 
is consequently along these dikes much crushed and broken 
ground, and it is in this crushed area that the mineral deposits 
of the district are located. 
The lamprophyres as well as most of the associated rocks 
are found between the 700 foot and 900 foot levels of these 
mines. All are extremely fresh and show little alteration to 
the naked eye. 
The igneous rocks described in this paper occur as dikes 
and stocks in the War Eagle, Josie, Iron Mask, Le Roi, and Le 
Roi No. I mines, and were collected by Mr. E. A. Strout, a 
mining engineer of Rossland. I am. indebted to Mr. Strout for 
the notes on the geologic occurrence of these rocks. They rep- 
resent all the sorts of rock observed in an underground survey 
of the above mentioned mines.* 
The numbers corresponding to Mr. Strout's type set of 
rocks, now deposited in the geologic collection at Stanford Uni- 
versity, are given with each description for convenience of ref- 
erence. 
LAMPROPHYRES. 
Kersantyte. — This rock, (40 Rossland) Fig. i, occurs in a 
ninety-foot dike at the 700 foot level of the Josie mine, and is 
a black, fine grained rock with large crystals of biotite. It is 
rich in mica and has some hornblende, feldspar and magnetite. 
The biotite, present in great abundance, is brown in color 
and shows the characteristic wavy cleavage. In some cases it 
has formed secondary muscovite, giving up its iron as magne- 
tite. It is strongly pleochroic, changing from light to dark 
brown and has a maximum size of 1.2 mm. in length and .5 
mm. in width. 
The muscovite is perfectly clear, has very fine parallel cleav- 
age, and is highly colored in polarized light. 
The feldspar Avhich is in the ratio of about two to three to 
the biotite is largely labradorite, showing polysynthetic twin- 
ning, zonal extinction, and extinction angles varying between 
21° and 28°. It is weathered to calcite in some instances. 
Hornblende is present chiefly as phenbcrysts with a rather 
deep color and with pleochroism from light to dark green. The 
♦I am indebted to Mr. H. S. Coe, a mining engineer of Craig, Colorado, 
for the preparation of a number of slides and for assistance in the descrip- 
tion of some of the rocks. 
