110 SIERRA DE UMANGO 
likewise folded sandstones, appearing here in the so called „inter- 
montane zone". This zone is, as said, limited to the west and to 
the east by gliding planes, the western one dipping 45° W and 
showing a fault-overthrust to the east. The zone border is here — 
overthrusted by the edge of the crystalline basement block of the | 
Sierra de Umango ridge.. All the sediments sau in this zone, 
NINO MOM Y 
nae 
Pye 
aes 2 Ck NED aha DR 
HEINE I: il 
IH: RYAN 
TIER BS en Ir 
a a BEN ARSA EN ÅR 
i 
fat — Sa CAT aa N ie 
Fett: au 
sai dit en 
Ai 
Fig. 16. Part of the ,intermontane zone“, to the NNE from the sector between the mountains. The 
picture will show the various bendings of the continental strata. These are overlaid by the horizon- 
tally lying young’ (tertiary) conglomerate (horisontally striated). In the foreground an edge of the moun- 
tain block of the Sierra de Umango. Looking east-northeast. 
which runs between the mountain blocks of the Sierra de Umango 
ridge and the Cerro Potrero Viejo, are laid into strong folds, mostly 
upright ones. Also many faults do occur (see the figure 16). Out- 
ward the „intermontane“ section no folds are visible, but monoclinal 
dipping and bending of-the strata. 
Close to the eastern border of the ,intermontane zone“, on the 
southern end of the Cerro Potrero viejo, there is a strongly folded 
complex of alternating lower Gondwana sandstone and slate. Here 
the folding may be regarded as an overthrust-phenomenon over 
