ransome.] METAMORPHISM OF THE COUNTRY ROCK. 
125 
can be recognized, but not uncommonly these, too, have vanished, and 
the rock has become a white granular aggregate resembling a fine- 
grained quartzite. Of such origin and character is most of the 
so-called "quartz" of the Red Mountain mines, which forms the sili- 
ceous knobs in which many of the ore bodies outcrop. 
The mound at the White Cloud mine may be taken as a typical 
example of such a knob or knoll. It is elliptical in plan and about 
50 feet long, trending K 10° E. It rises about 30 or 40 feet above the 
general slope of the hill, and is composed of bleached siliceous rock 
which occasionally shows 1 faces of breccia structure and which is 
evidently an altered form of the Silverton andesitic breccia. It con- 
tains considerable very finely disseminated pyrite. 
A thin section of this rock shows a finely crystalline, rather turbid 
aggregate of quartz, kaolin, pyrite, rutile, and some minute inde- 
terminable minerals. Some outlines of former phenocrysts are rec- 
ognizable in ordinary light, but these disappear between crossed 
nicols. The quartz grains are very irregular in outline and intricately 
interlocked. They are full of minute inclusions of kaolinite, rutile, 
pyrite, and other minerals too small for determination. The kaolin 
occurs in bunches showing the characteristic foliated aggregation of 
the individual scales, and the usual low double refraction. 
A chemical analysis of this rock, from a specimen taken in a short 
tunnel in the knoll, is here uiven: 
Analysis of altered andesitic breccia from White Cloud mine. 
[George Steiger, analyst.] 
Constituent. 
Per cent. 
Constituent. 
Per cent. 
Si0 2 - 
v.. 19 
5. »'•» 
.23 
. 25 
None. 
.27 
None. 
None. 
.46 
3.07 
TiO, 
CO.. 
63 
Alo0 3 - 
FO..O-, 
P..O- 
07 
FeO 
so 3 - 
-!<> 
MgO 
MnO 
CaO 
BaO__ 
FeS 2 - 
.07 
NiK) 
3.43 
K.O 
HoO--.- 
99.92 
HoO+ ._ 
No analysis of unaltered rock is here available for comparison, and 
it is not possible to determine accurately the additions and subtrac- 
tions to the original rock which have resulted in the metamorphosed 
facies. It is evident, however, that either the alumina has been 
very greatly reduced or the silica has been enormously increased. In 
all probability there has been some removal of alumina and a large 
addition of silica. Ferric and ferrous iron have been partly removed 
and the residue has been changed to pyrite. Lime has been almost 
all carried away and soda and potash have been wholly removed. Car- 
