50 STUDIES IN GEOLOGY, No. i 



Except for the absence of gypsum, these rocks are 

 strikingly similar to the Ramos. That they represent a 

 younger series of rocks unconformably overlying the two 

 older series, is clearly shown by the relations in the Cerro 

 Corocoro. There are considerable variations in strike and 

 dip from place to place, but the series has a prevailingly 

 easterly or southerly dip on the Cerro Corocoro. The out- 

 crop of a prominent sandstone horizon shown on the geologic 

 map has a trend across the strike of the fault and the Vetas 

 and Ramos. The latter geologic features have been followed 

 in the mine workings nearly I km. south of the point on the 

 north side of Cerro Corocoro where they are covered up by 

 this overlying series. There is no mineralization at the sur- 

 face above the Guallatiri Grande tunnel nor at the Challcoma 

 shaft, yet in depth the fault, the Vetas, and the Ramos are 

 encountered. The Desaguadero series is younger than 

 either of the other series, it is subsequent to the Corocoro 

 fault, and subsequent to the mineralization. 



On Cerro Corocoro the Desaguadero series lies uncon- 

 formably over the Vetas, but to the southwest, the two series 

 are separated by a fault. Along the fault line the Vetas beds 

 are distorted and often dragged to the extent of reversing 

 their normal position to an easterly dip. As the fault 

 reaches the flanks of Cerro Corocoro, east of the main trail 

 at the southwest edge of the city, the outcrops become 

 obscure and it can not be followed farther. It seems to die 

 out before reaching the Corocoro fault for there is no 

 evidence of it in the Remedies mine. The fault is a break 

 along which the Desaguadero beds moved down with respect 

 to the Vetas, and is probably a reverse fault that accompa- 

 nied the folding and tilting subsequent to the deposition of 

 the former series. 



AGE OF THE DESAGUADERO SERIES 



The rocks of the Desaguadero series failed to yield any 

 organic remains, although they were carefully examined on 

 Cerro Corocoro, along the railroad between Corocoro and 



