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CRYSTALLINE BASEMENT 23 
thinned out and torn. The banded appearance of the amphibolites in 
the granitic injection zones of the more central parts of the area, 
o— as will be demonstrated later on — a very common phenomenon, 
is produced principally by an exfoliation-process of thicker ampbi- 
bolite layers by way of concordant granitic injection. Only in the 
zones of the „schistes lustrées“ the amphibolite sills occur in a more 
preserved stage, a fact due principally to the almost complete ab- 
sence of granite veins. An exception from ihis rule is to be found in the 
hills of the Cerro Asperecito, the Cerro Pintado and the Cerro Tupe 
in the Vinchina valley, where the amphibolite layers are intensely 
penetrated as to form an arterite (Sederholm), due to the imme- 
diate vicinity of the Famatina batholith. But the appearance as a 
whole, the concordant alternance between the schists and the sills, 
is still conserved here too. 
On studying the microstructure of the basic rocks, it is seen, that 
hardly in anyone part of the area a primary or an almost primary 
one occurs. The structure is either a kataclastic or a recrystallized 
one, because undergone all diastrophic movements of different times. 
The basic rocks may here be divided into three groups, as follows: 
1) Concordant sills of amphibolites. 
2) A peridotitic sill rock (local occurrence). 
3) Basic, kataclastic schists of doubtful origin. 
Tho these belongs still an isolated type of porphyritic character and 
of local occurrence too. While the rock is of less basic character, 
it will be described apart from the enumerated types. 
1) Concordant sills of amphibolites. 
The greater part of these amphibolites occurs, as mentioned, 
as mighty, alternating sills in the mica schist zones, where they 
often appear with astonishing regularity. They are also found in 
the quartzitic schist masses and in the limestone banks, where the 
Sills are generally thinner. The contorted appearance of the Jimes- 
tone has already been mentioned. 
