86 SIERRA DE UMANGO 
sandstone in regular, alternation with quite a coarse conglomerate, 
containing well waterworn pebbles. At the fault-line itself these 
layers stand vertically, but to the south their position becomes 
more gentle-dipping with westerly inclination, while to the north, 
on ‘the western border of the Jaguel depression, the dip is toward 
the east. The longitudinal extension of these strata reaches pro- 
bably far into the Catamarca mountains, and southward at least 
to the northern head of the Precordillera of Guandacol. 
There are following mountains composed of these rocks: from 
north to south the Cerro Punta Negra, the Cerros de Agua de la 
Piedra, the Cerro La Estaca and the eastern part of the Cerro 
Descubrimientos. The general strike of the strata is to the north, 
but a trend toward the northeast is observed in the northern part 
of the zone. 
The zone marks the eastern border of the Cordillera in these 
regions, except to the west of the Cerro Cacho, where the first 
ridges built up by these series still belong to the topographical 
unity of the Cerro Cacho. Then follows to the west of these rid- 
ges the Pampa de Leoncito. Some small hills there rise over the 
gravel plains of this plateau and are composed of the clastic strata in 
question. The Cerro de Leoncito, bordering to the west the named 
pampa, is, however, differently composed, as is seen already from 
a greater distance. This region was studied by Rassmuss. 
The sandstone-conglomerate complex lacks every lithological simi- 
larity with the continental series of the Umango area. It is consi- 
dered by Rassmuss of Gondwana age!. In any case the strata 
are of postgranitic age, because they dont show any influence of 
granitic intrusion, which outcrops in the immediate vicinity, amidst 
the Cerro Cacho crystalline schists. The strata have a purely 
clastic habit. The concordance betweem the schists and these 
strata is thence only a tectonical juxtaposition of tertiary age, pro- 
bably of a similar kind as the „conformities“ between schists and 
1 Verbal communication. 
