130 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
and some undetermined minerals in minute grains are also present. 
At the Mystery claim, on the summit of Anvil Mountain, the rock 
(rhyolite?) has been changed to a nearly white, rather porous mass 
showing no traces of original igneous structure. Under the micro- 
scope it shows faint outlines of former phenocrysts, which become 
nearly invisible between crossed nicols. The rock consists chiefly of 
quartz and alunite in a fine-granular aggregate, with a little kaolin 
and rutile. At John Roland's tunnel, about 1^ miles southeast of the 
Mystery claim, an opportunity was presented for studying some of 
the steps of alteration. About 150 feet from its mouth the tunnel cuts 
through a very irregular vein-like mass of kaolin and continues beyond 
it for 200 feet or more. Near the breast the rock, although altered, can 
be recognized as an andesite, or closely related rock. It is greenish 
gray in color and shows outlines of small feldspar phenocrysts. 
Under the microscope, although the original porphyritic structure is 
partly preserved, the rock is seen to be completely altered. The phe- 
nocrysts of plagioclase are changed to sericite and quartz, while the 
augite and perhaps other dark constituents are represented by pseu- 
domorphs of chlorite and calcite. At about 150 feet from the fissure 
the country rock is already bleached to a light greenish-gray tint and 
the original texture partly obliterated. Under the microscope it is 
seen to be a secondary aggregate, consisting chiefly of sericite, quartz, 
and calcite, retaining, however, outlines of the original porphyritic 
structure. About 45 feet from the fissure the rock is nearly white 
and shows very faint traces of original texture. In general appear- 
ance it is identical with most of the bleached and metamorphosed rock 
of the Red Mountain Range. Microscopically examined, the outlines 
of former phenocrysts are distinctly visible, but the whole rock is 
recrystallized to a very fine aggregate of quartz and sericite with some 
leucoxene (rutile). The former feldspar phenocrysts are now nearly 
pure sericite Lastly, a specimen taken from the wall of the fissure 
is a nearly white, compact rock in which close scrutiny fails to detect! 
any vestige of primary structure. Under the microscope the rock 
appears as a finely crystalline aggregate consisting of quartz and seri- 
cite, with a little brownish isotropic material occurring in minute vein- 
lets. Recrystallization in this case has not only been complete, but 
there has been such thorough rearrangement of the crystallizing mate- 
rial as to obliterate all traces of primary structure. The alteration 
has plainly been accompanied by removal of iron, lime, magnesia, and 
probably other constituents. Whether alumina has been removed is| 
an open question, but the fact that the fissure from whence the meta- 
morphosing solutions penetrated the inclosing rock is itself filled with 
a vein-like deposit of kaolin shows that at some depth both potash and 
alumina have been removed from the country rock and concentrated 
as kaolinite within the fissure walls. 
The conspicuous metaniorphism of the Red Mountain region has 
