CRYSTALLINE BASEMENT 21 
The Precambrian Basement. 
| Above we have presumed, that the sedimentary members of the 
a Umango structure are derived from an old surface, composed pro- 
| bably of chiefly acid crystalline rocks, i. e., a precambrian basement. 
The next question which arises, is where to find this basement, and 
ii it still exists in this part of the Republic. 
The Umango schists are rooting in an irruptive granitic mass, 
the Famatina batholith. Everywhere to the east the schists are boun- 
ded by this granite with its many dikes and embayments. Thence 
a precambrian complex is not visible here. Going farther to the 
east, into the Famatina mountains, one meets with complexes of 
the mentioned cambrosilurian schists, on all sides surrounded by 
the irruptive granite (see the sketch map, page 30). Here also an 
older element is lacking. Bodenbender mentions, that the Fa- 
_ matina granite extends eastward to the very foot of the Sierra de 
Velazco, a mountain mass rising to the east of the Chilecito valley. 
On the western slope of this mountain an old gneissic rock extends 
in a northerly direction as already recognized by Stelzner and 
Brackebusch, and fixed on the map of the latter. The gneiss shows 
an itruptive contact against the Famatina granite. On the crest of 
this Sierra we find again the same younger granite (see the corres- 
ponding profile of Stelzner), probably only a branch of the great 
Famatina intrusive body. This old gneiss may probably be regarded 
as the precambrian basement. A confirmation of this statement will 
be found in the relations further to the north, in regions of the 
province of Catamarca. Here is found a mountain system to the 
east of the above named valley of Fiambalä, more closely inves- 
tigated by W. Penck. This terrane consists of old schists and 
gneissic rocks with younger granitic intrusions as in the Sierra de 
Velazco. Between the schists-gneisses and the western element, 
i. e., the continuation of the Umango structure, there occurs a large gra- 
nitic body, according to Penck, belonging to the Famatina batholith.! 
1 See the map of W. Penck (1920). 
