06 SIERRA DE UMANGO 
biotite plays the part of „phenocrysts“ and greater lenses, while 
the fine granulated mesostasis is composed of quartz and sericite.! 
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4 
E) GENERALITIES ON THE GEOLOGICAL POSITION OF THE | 
SIERRA DE UMANGO AREA. 
As a consequence of the scarceness of our knowledge of the ~ 
geology of the vast area composed by crystalline, partly sedimen- 
tary and partly igneous, rocks of the central part of the Argentine 
Republic, appearing in the so called „Sierras pampeanas“, reaching — 
to the very border of the Andes, it will be a difficult task by a 
limited surveying in this area (the Sierra de Umango) to explain 
any broader tectonical and structural relations. Working in the 
Sierra de Umango area the writer did not get any occasion to 
make excursions into the surrounding countries so as to obtain 
more general views. The existing litterature and the maps of the 
neighbouring districts, lately prepared, have, however, facilitated an 
attempt to a somewhat broader synopsis, although the results may 
be in many respects only hypothetical ones. 
The general orientation of the metamorphic schists in the „Sier- 
ras pampeanas“ has been fixed as running nearly N—S over wide © 
areas. Also in regions near to the Andes this crystalline basement 
shows a similar behaviour. The schists of the Sierra de Famatina, 
the Sierra de Umango and also of the Sierra Pié de Palo farther 
south are roughly trended into this general orientation. 
Granitic bosses and batholiths of various extension are intruded 
into the gneiss and schist complexes at various times and have 
caused a regional metamorphic, and in many cases ultrametamorphic 
change of the preexistant rocks. Similar kind of abyssal metamor- 
phism has overgone, as has been shown above, also the Famatina— 
Umango schists, principally by intrusion of the Famatina batholith. 
1 See also Plate VII, figg. 1 and 2. 
