326 Palmer — Notes on the Andes of N. W. Argentina. 



westernmost is composed wholly of Paleozoic schists for its 

 entire visible height of a couple of hundred meters. The 

 easternmost of these spurs is, on the other hand, composed 

 entirely of red sandstone. There is a great deal of brecciated 

 material in the gully between the two spurs. The hypothesis 

 that this is a contact due to original sedimentation is untenable, 

 for the red sandstone dips westward into the metamorphics, 

 and the necessary thickness of red sandstone can not be 

 accommodated by a reversal of dip in the zone covered by the 

 breccia. 



Fig. 8. 



Fig. 8. Looking eastward from the middle of the Calchaqui valley to the 

 Curnbres del Obispo opposite La Poma. Note the mature upper slopes, the 

 smooth middle slopes, and the very young gullies in the lower slopes. The 

 folded Jurassic red sandstone is seen in the middle ground and the crumpled 

 and fissile Paleozoic metasediments in the background. This figure is to be 

 compared with figure 9. 



Owing to the conditions of work and the rough topography 

 it was impossible to examine the nature of the contact between 

 the Jurassic red sandstone and the Paleozoic metamorphics at 

 other points. Below are given several arguments of circum- 

 stantial nature, which have led to the conclusion that both of 

 the marginal faults extend the whole length of the valley. 



The Cumbres del Obispo, 1200 to 2100 meters higher than 

 the valley, lie on the eastern side of the Calchaqui depression, 

 and their whole slope towards the valley is very smooth. The 



