ERSTER EEE 
ARE FF 
DETRITIC FORMATIONS | 85 
Umango crystalline complex, on the watershed between the Que- 
brada Piedra Pintada and the Quebrada Cacho. In the former lo- 
cality an overthrust from the west is to be noted and also dynamic 
phenomena. Here the sandstone is of red colour and carries con- 
_ cordant sheets of a basic tuff. Conglomeratic layers do also occur. 
In the latter locality the red sandstone layers stand vertically bet- 
ween vertical crystalline schists on the eastern side and strata of 
a graywacke and conglomerate series in similar position to the 
west. 
At the western entrance of the Paso del Cordobés (Quebrada del 
Cordobés) there are, going east, on the left hand a pale yellowish 
sandstone lying almost in a horizontal position against the moun- 
tain slope, consisting of old crystalline rocks. The sandstone has 
purely white shades and contains conglomeratic interstratifications. 
The whole character shows a similarity to the lower Gondwana. 
On the right hand there is a steep, high wall of old crystalline rocks, 
the sandstone remnant is thence evidently downsunk and preserved 
here in spite of the great absolute height of the locality. 
At the eastern foot of, the Cerro Villa Union I observed on the 
trail from Villa Union to Maz a red sandstone immediately at the 
crystalline rock-wall, well exposed in the quebrada-profiles. This 
small outcrop is evidently the only visible remnant of a vast sunk 
sandstone area, occupying the floor between the named Cerro and 
the hills of Las Ramaditas and covered with the mountain gravel 
sheets. To which extension the lowland to the north from here 
may have a sandstone basement cannot be determined, because 
the alluvial fans from the mountain to the west cover all this ground, 
The clastic complex west off the Umango area. 
As has been already stated, the Umango-Cacho crystalline base- 
ment complex is bordered to the west by a great fault-line running 
north and separating it from an extensive series of steeply inclined 
 castic strata, composed, as observed, essentially of a graywacke-like 
