i 
2 
2: 
a 
RS if 
BR 
RR EP U > Fa a 
ae ep ng ee 
ee te ee RO 
t 
i ae A då 
eT 
ee ee 
Y 
IR ER 
Euer; 
SEE NONE DEE DONE EE 
CRYSTALLINE BASEMENT 53 
microscopical slide of this type demonstrates a very fine granulation 
of the quartz and feldspar components. The secondary grains are 
all isometric in shape and the parallel structure is less conspicuous 
than in handspecimens. Flat lenses of a secondary, opaque substance 
can be seen, probably the last remnant of some mafic minerals 
(amphibole?). 
In the Cerro Cacho complex all the granitic stocks of longitudinal 
shape and the concordant dikes have been affected by the tertiary 
and partly also by some older movements. The most intense cru- 
shing appears near to the western border of the complex, where 
the bordering fault-line runs (to the west from Quebrada Cacho and 
Quebrada Agua de la Piedra). On the eastern slope of the moun- 
tain, where the seleniure mining area is situated,’ there is a large, 
longitudinal stock of aplitic granite, penetrating amphibolite schists 
and limestone banks. The granite has been transformed into gneiss 
by pression phenomena. That the pression here really belongs 
to an older phase is seen from the circumstance, that the granite 
has been folded simultaneously with the surrounding schists, and 
is penetrated by a dike of white pegmatite. A handspecimen of 
the red granite shows a distinct parallel structure, but not a schistose 
one. The mineralogical composition of the rock seems to be that of 
an eutectical mixture. The graphic texture has indeed been torn 
off. But in spite of the strong pressure the quartz and feldspar 
components have not been mingled together to a higher degree, a 
fact, proved also microscopically. The microscopical examination 
shows, that the resulted grain of the rock is a ,double“ one, that 
is, every individual has been broken off into smaller fragments holding 
to some extent their original position. This is the case especially 
with the feldspar grains, while the quartz mostly forms a cementering 
or filling mass between the feldspar aggregates. This quartz mass 
has a dynamical flow arrangement, but generally with an oblique di- 
1 See the concluding chapter, Part II. 
