TERTIARY TECTON ICS 109 
4 of pigmentation by ferric oxide dust, as may be confirmed micros- 
 copically. Between crossed nicols the slide is only dull transpa- 
rent, or nearly black. This mass seems to contain feldspar as 
principal component. Also larger feldspar individuals occur with a 
tabular development showing a perthitic structure. Regarding the 
„parallel extinction“ in cuts perpendicular to M the feldspar seems 
| to be a potash one. 
- 6) THE TERTIARY AND QUATERNARY GEOMORPHOLOGICAL 
DEVELOPMENT. 
a) A FIRST TERTIARY OROGENETIC PHASE. 
Folding tectonic in the Sierra de Umango area. 
As has been shown several times by Keidel (1910, 1914) a, o. the 
Argentine-Chilean Cordillera with its great) pile of mesozoic sedi- 
ments and volcanics was affected by a first folding process during 
_ middle tertiary time, antecedent to a phase, when the present al- 
pine relief was formed. The two phases of diastrophism have been 
distinguished one from another by way of morphological evidences. 
While a strong tangential pressure from the west affected the 
andine geosyncline during the first phase, it may be assumed, that 
the ,Foreland“ to the east, that is, the western margin of the pam- 
pean sierras-area also came into the zone of the pressure influence. 
Studying the tertiary tectonics in the foreland, one really finds in 
- many parts folding phenomena, caused by overthrusting from the 
west. The first informations on these movements were brought by 
W. Penck (1915) from Catamarca, where the sandstones to the 
west of the valley of Fiambalä are folded in part.! Later on 
Bodenbender (1916) has mentioned similar phenomena also from 
the Nevado de Famatina. In the Sierra de Umango area there are 
1 About the Famatina range (stretching northward to Catamarca) he says (page 
649): „Junge, tertiäre Faltung charakterisiert die Famatinakette im Gegensatz zu 
den östlichen Gebirgszügen.“ 
