46 . SIERRA DE UMANGO 
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that the lower permian tillites rest directly over this twice granitized | | ut 
basement. 
Ch 
As was already stated in short, the white granite-syenite intrusions fj 0!” 
are met with principally in the western parts of the Umango area, 
outcropping as broader zones in the Sierra de Umango ridge and 9" 
the Cerro Potrero Viejo. The whole intervening space between the 
former ridge and the Cerro Cacho is also rich of such dikes. In 
the last mentioned mountain there are similar dikes too, but a red 
granite, however, dominates. Only in one ‘part the intrusion of Au 
stance makes it evident, that the intrusion was contemporaneous 
with the tangential pressure. 
The folding and the banding are also phenomena characterizing | hi 
the appearance of the white granite-syenite. To the east, in the | pal 
region of the Famatina batholith there are no signs of lateral stress, conc 
and a younger granite seems to be lacking there too. Boden- | 
bender mentions no occurrence of this intrusive from there, and § 
as to myself, I have never discovered any dikes of this rock inside | Fin di 
the batholith. 
Nothing further are known regarding the occurrences of youn- | 
ger (post-Famatina) granites in the pampean sierras-area, be- 7 
cause the study of the chronology of the old intrusions in this area : 
is still a task never touched upon. According to a verbal com- 
munication by Rassmuss, he has seen traces of a younger intru- — 
sion in the Sierra de Velazco, a white granite crossing the red one, the ~ 
latter corresponding to the Famatina granite. 
a) MANNER OF INTRUSION OF YOUNGER GRANITES AND SYENITES. 
As already stated, the younger intrusives show a less conspicuous | N: 
abyssal character than the Famatina red granite, and they depend | 
to a considerable degree in their manner of intrusion on the struc- — 
