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



The red sandstone between the marginal faults of the valley 

 is slightly folded and faulted internally. It has been thrown 

 into open anticlines and synclines, whose axes trend north and 

 south, i. e. parallel to the length of the valley. The steepest 

 parts of the flanks of the folds dip about thirty degrees, but in 

 the lesser folds the dips become in places as steep as sixty 

 degrees. In a few cases thrust faulting has taken place, as for 

 example at a point near Cerrillos illustrated in lig. 5. The 



Fig. 5. 



Fig. 5. Small overturned fold and small thrust fault in the Jurassic red 

 sandstone near Cerrillos. The fault line is indicated by the arrow as it is 

 obscured in part by debris. 



photograph shows a cliff about one hundred and twenty feet 

 high, exposing in section a thrust fault and a monoclinal, over- 

 turned fold. The beds are offset about two meters by the 

 fault and about three meters by the fold. The average position 

 of the beds on the long flank of the fold is N. 40° E., with a 

 dip of 18° NW. 



The broader structure of the red sandstone of the valley is 

 shown in fig. 6, reproduced from a sketch made looking north 

 from La Poma. The broad anticline and syncline are diagram- 

 matically distinct in the held and are but slightly accentuated 

 in the sketch. The photograph and sketch (figs. 5 and 6) 

 show how slight has been the disturbance of the red sandstones 



