46 STUDIES IN GEOLOGY, No. i 



Steinmann makes the Vetas equivalent to the lower 

 member of his Puca sandstone and the Ramos to the middle 

 member, and consequently the Ramos younger than the 

 Vetas and on the downthrow side of the fault. The fault 

 itself he considers an overthrust of the Vetas on the Ramos 

 with a very steep westerly dip and to disappear to the south 

 by passing over into a normal anticline. Since the Corocoro 

 rocks are not his Puca sandstone, his conclusions are 

 invalid. 



Singe wald and Miller state that the strike of the Vetas 

 and the strike of the fault are the same, about N.,3O W., 

 and that the dip of the fault is a little steeper to the west 

 than that of the Vetas. The strike of the Ramos is a little 

 more northerly than that of the fault and as they dip easterly, 

 successively lower beds come to the surface northward along 

 the fault plane. The Ramos have an upward drag close to 

 the fault plane which steepens their dip in its proximity and 

 indicates a downthrow on their side, or a reverse fault. 



Lincoln says the Corocoro district consists of a faulted 

 anticline with northerly strike and with the beds dipping 

 away from the fault in both directions. The strike of the 

 Vetas is nearly parallel to that of the fault, but the Ramos 

 diverge from the fault going northward exposing succes- 

 sively younger beds. He thinks the two series of rocks are 

 the severed portions of the same group of copper-bearing 

 sandstones. The measured sections demonstrate the error 

 of the last conclusion. 



The Corocoro fault is first encountered on the surface 

 west of the Santa Rosa shaft on the lower slope of Corocoro 

 mountain above the town of Corocoro. Underground in the 

 Cerro Corocoro it can be followed in the workings of the 

 Remedies, Guallatiri Grande, and Challcoma mines, a dis- 

 tance of i km. to the south, that is, to the southern limit of 

 the mine workings. It is covered at the surface over this 

 stretch by the Desaguadero series. Northward from the 

 Santa Rosa shaft the fault can be easily followed on the 

 surface along the lower slope of the ridge paralleling the 



