82 SIERRA DE UMANGO 
At the southern end of the Sierra de Umango ridge the ,inter- 
montane zone" shows a remarkable virgation. The western half 
of the zone bends into a sharp curve to the west along the sout- 
hern head of the ,crystalline* mountain block, while the eastern 
half continues in southerly direction to the Precordillera of Guanda- 
a eS ae Zu 
col, here passing over into the tertiary structure. Between these — 
two branches lies the tectonical throw of Nacimientos -- Zapallar, 
filled out by dislocated, young tertiary gravels. 
The eastern branch has entirely the same appearance as the just 
described ridge between the Vinchina valley and the Jaguel de- 
Fig. 13. Tertiary arenaceons strata dipping W to the N from Sierra de Umango, 
at the E border of the Jaguel bolson. S. U. in the distance. Z = intermontane 
zone with folded sandstones. C= young conglomerate in horizontal position. 
pression. The Cerros de San Antonio, as this southern ridge has 
been named, forms too a high bluff of several hundred meters to the 
east running SSW and also almost S, at the same time bordering 
the Zapallar depression from the Carrizal valley train to the east. 
The strata here show, like these in the northern ridge, a generally 
increasing dip towards the west, while the lithological character of 
the strata changes getting a softer consistence and a paler colour. 
h 
å 
The bluff on the eastern side shows the same brown, slightly dis- 
turbed layers as in the ridge to the north of the mountains (the 
stratigraphy of this bluff has been already more closely described ; 
on page 81). A good cut through the whole ridge can be obtai- 
i he ee ur Aue 
