100 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
ined under the microscope, shows the rock to be a coarse-grained 
normal soda granite, with much anhedral quartz and anhedral feld- 
spar, largely microperthite, with some few grains of microcline. A 
few small flakes of brownish-green hornblende and some small grains 
of magnetite were also seen. 
White aplite-granite occurs in veinlets and irregular masses intru- 
sive in the granite, but none was observed close to the veins. 
ORES AND VEINS. 
The ores consist of cassiterite, or oxide of tin, with wolframite 
(tungstate of iron and manganese) in a gangue of quartz. Specimens 
of nearly pure cassiterite weighing several pounds have been found 
on the surface, and this mineral occurs in the quartz, either alone or 
associated with wolframite. The most abundant ore is a granular 
mixture of tin ore and quartz which resembles a coarse granite and 
corresponds to the greisen ore of European tin deposits. Pyrite 
occurs rarely in the eastern exposures of the vein, but appears to 
constitute the bulk of the metallic contents in exposures seen in the 
westernmost openings. These ores occur in well-defined veins, which 
run up the slopes nearly at right angles to the direction of the range, 
the strike being approximately east- west and the veins dipping steeply 
to the north. Three veins have been discovered, all of which have 
been exposed by open-cut work and by pits for several hundred feet 
in length. The most northerly vein is traceable along the surface for 
a distance of about 1,200 feet. The middle vein lies about 300 feet 
south of the east end of the northern one, but apparently converges 
westward toward the northern vein. The southern vein, which is the 
smallest of the three, lies about GOO feet farther south. 
The veins exhibit the usual characters of the European tin veins, 
notably those of Cornwall, England, their clearly defined fissures show- 
ing a central core or lead of coarse quartz, sometimes containing tin 
ore, and flanked on either side by altered rock in which the tin ore 
replaces the feldspar of the granite. Where this metasomatic replace- 
ment is complete the ore shows a mixture of cassiterite, with or with- 
out wolframite and quartz. Where the replacement is only partial the 
greisen ore fades off into the unaltered granite. A cross section of 
the veins shows, therefore, the same phenomena seen in Cornwall. 
The central mass of quartz corresponds to the " leader" of the Cornish 
veins. It is composed of massive, coarsely crystalline quartz, some- 
times showing comb structure, and it is clearly the result of the filling 
of the open fissure by quartz. The adjacent ore-bearing material is 
a replacement deposit in which the mineral solutions have substituted 
ore for the feldspar of the granite by metasomatic action; in other 
words, the main mass of the ore occurs alongside of a quartz vein, and 
is due to the alteration of the granite forming the walls of the fissure. 
In general, the ore passes into the granite by insensible transition and 
there are no distinct walls. 
