COROCORO COPPER DISTRICT OF BOLIVIA 45 



than the Vetas is a more probable assumption' than the 

 reverse. Farther than this the paleontologic evidence does 

 not carry us. 



The relations between the two formations could be 

 determined, therefore, with certainty only on structural 

 grounds, but here again difficulties are encountered. 



Forbes gives a cross-section and a ground-plan diagram 

 (p. 41) to illustrate his conception of the relations of the 

 Vetas and Ramos. According to his cross-section both series 

 represent approximately the same horizon, being separated 

 by a vertical fault plane with the downthrow on the Vetas 

 side. The incorrectness of this stratigraphic interpretation 

 is demonstrated by the descriptions of the measured sections. 

 Although the cross-section shows the Vetas on the down- 

 throw side of the fault, Forbes says the dip of the Ramos 

 decreases rapidly from 80 at the fault plane to 30 a short 

 distance away from it,, "showing that a sort of bend or curve 

 had taken place in the beds on settling down or coming to 

 rest after the dislocation." This evidence would make a 

 downthrow on the Ramos side the more probable. The 

 ground plan shows the Vetas parallel to the strike of the 

 fault and the Ramos diverging from the fault at a small 

 angle but shows the divergence toward the south instead of 

 toward the north. The latter is doubtless an inadvertant 

 error for in the text he gives the strike of the Vetas ranging 

 from N. 35 to 45 W. and the Ramos from N. 20 to 35 

 W. 



Mossbach describes the edges of the Ramos upturned 

 along the fault plane and believes the Vetas were pushed 

 over the Ramos. The Vetas are considered the older and 

 more consolidated beds and the Ramos the overlying and 

 less consolidated beds of the same series of strata. 



Sundt believed the Vetas an older series of rocks than 

 the Ramos, because, as he says, the Ramos rest on top of the 

 Vetas and surround them to the southeast, south, and west. 

 These are the relations of the Desaguadero series which is 

 described farther on to the Vetas and he has seemingly 

 confused it with the Ramos. 



