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



The Amount of Displacement. 



as 



The amount of the faulting must be of the same order 

 the height of the mountains on either side of the valley, pre- 

 suming that the region had moderate relief at the time when 

 the red sandstones were deposited and that the faulting belongs 

 to the cycle of uplift and erosion which has made the present 

 mountains. Were the Jurassic red sandstones deposited in 

 what was already a rather narrow canyon, the amount of the 



Fig. 9. 



Fig. 9. Looking eastward from tlie middle of the Calchaqui valley to 

 the Cumbres del Obispo six or eight kilometers north of La Poma. Note 

 that the very young gullies in the ridge in the background are restricted to 

 the lowermost portions of the mature slopes. Ledges of Jurassic red sand- 

 stone in the foreground dip under the camera. The well stratified rocks 

 across the valley are also of Jurassic red sandstone. The upper slopes and 

 the snow-capped peaks in the background are of Paleozoic metasediments 

 Compare with figure 8. 



throw would be lessened. On the other hand, if erosion has 

 been more effective on the tops of the mountains than in the 

 valley, the throw may have been greater than the present 

 height of the mountains. Presuming that these two factors 

 partly counterbalance each other, the height of the mountains 

 must be an approximate measure of the amount of throw of 

 these faults. 



