CRYSTALLINE BASEMENT - 
area) indicates, that the folding power at different times of pre- 
| cambrian and older palaeozoic periods was working almost in the 
same or in opposite directions. That fact increases the difficulty of 
‘ recognizing structures of different ages in this region. 
| As a matter of fact, resulting from the foregoing treatment, the 
_ Famatina and the Umango schist complexes must be considered as 
older palaeozoic members, by downfolding incorporated in the old 
basement and strongly metamorphosed by subsequent granitic in- 
_trusion. The granitization belongs to a period, antedated to the 
time of the permian orogenetic phase. The lower Gondwana rests, 
as we have seen, with a great unconformity on the granite intruded 
schists. Thence, the Umango structure cannot, as Penck believes, 
be any continuation of the Precordilleran structure, but is an older 
one. The juxtaposition of these two structures is caused by later 
movements (the permian [Precordilleran] and also the tertiary [Cor- 
dilleran]). In the Umango area the deep geological level of the 
pampean underground and the ,Sierras pampeanas“ is thence 
brought side by side with the more supercrustal masses of the 
Precordilleran palaeozoic formations. 
Because the position of the Umango area in the immediate front 
of the permian and tertiary andean folding zones, the area in question 
has played the part of a „foreland“ during at least two diastro- 
phic phases and has consequently also undergone tectonical influences, 
differing from these of the , Sierras pampeanas“ in general. 
This circumstance makes the Umango area to an interesting field 
for studying mutual petrographical and tectonical relations, as the 
foregoing chapters may have illustrated. 
