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the plagioclase. The amphibole shows in the prismatic zone a maxi- 
CRYSTALLINE BASEMENT 25 
mal extinction angle of nearly 20°, the normal one of ordinary amphi- 
boles. The pleochroisme varies between grassy-green and greenish- 
yellow. The prismatic cleavage is well developed. The plagiocla- 
se is highly granulated by the dynamic influences, forming relatively 
small allotriomorphic grains. Albitic twinning lamellae are not well 
_ developed, so that measures of the extinction angles were difficult 
_ to realize. Biotite is a more accessory constituent. It is, hovewer, 
_ visible in handspecimen. Quartz is very scarce. The rock structure 
as a whole is distinctly schistose, because the amphibole individuals 
have been broken up in elongated fragments, following the 
prismatic cleavage. These fragments have also been arranged in 
_ subparallel lines. It may be mentioned, that the c-axis is parallel 
_ oriented to the general schistosity planes and also the biotite flags. 
The plagioclase grains are independent of the schistosity and form 
a finegrained matrix between the elongated constituents. 
The crystalline hills of Las Ramaditas on the eastern side of the 
Cerro Villa Union show, that the amphibolites play here a very im- 
portant part, forming whole hills and ridges. The dark masses of 
this rock are distinctly crossed in various directions by granitic and 
_ pegmatitic veins of red colour, representing a typical apophyse zone 
of the Famatina batholith (see later on). The amphibolite is here 
always highly recrystallized with a well developed parallel struc- 
ture. The sills lie concordant between quartzitic and thinner li- 
mestone layers. 
Near to the west from the Vinchina valley too, on the eastern slope 
of the Cerro Potrero Viejo,! where banded rock complexes predomi- 
wate, the amphibolite layers are very abundant, playing an important 
part in the mentioned banded structure. The amphibolite is of a 
thinner appearance, because of the concordant penetration with granite 
veins. The rock is not only recrystallized, but also partly absorbed 
_ (lateral banding by assimilation, a phenomenon described later on). 
1 Also named Cerro la Pampa. 
