COROCORO COPPER DISTRICT OF BOLIVIA 37 



carious line of reasoning. He believed that the Ramos lie 

 on top of the Vetas and surround them to the south and east 

 and hence represent a younger series. He was the first to 

 call attention to the trachytic material contained in the rocks 

 and used it as a basis for arriving at their age. Trachytes, 

 he says, have always been considered Tertiary in age and 

 never older. Hence the rocks which include the trachytic 

 fragments must be not older than Tertiary or there must be 

 older than Tertiary trachytes. In support of the latter he 

 cites examples of Cretaceous trachytes in Chili and Argen- 

 tina. Consequently he concludes that the Vetas are either 

 Cretaceous or Tertiary. Because of the thickness of the 

 Vetas and because of their uplift, folding, and depression 

 before the deposition of the Ramos, he considered the latter 

 definitely Tertiary. He believed that the Macrauchenia 

 skeleton was found in place, but doubted Huxley's post- 

 Pliocene determination. 



Dereims says he nowhere encountered fossils which per- 

 mitted a scientific determination of the age of the Corocoro 

 rocks, but he assigns them to the Permian on the basis of 

 their petrologic facies and because he believed them to lie 

 immediately above the Carboniferous. Their red color and 

 cupriferous character are to him worldwide Permian char- 

 acteristics. 



Steinmann also fell into error through correlation on the 

 basis of lithology. He mentions no fossils and says he was 

 unable to substantiate the occurrence of carbonized conifer 

 wood described by Forbes and others. He was aware of 

 the fact that red sandstones were deposited in Bolivia at 

 various periods from Silurian to Quaternary. The thickest 

 and most widespread series of these, he says, are his Puca 

 sandstone which he divides into three members. The lower- 

 most member consists of sandstone ; in the middle member 

 red clays prevail, frequently associated with gypsum and 

 often rock salt, and locally with limestones near the base; 

 and the upper member is, like the lower, prevailingly sand- 

 stone. Steinmann records Cretaceous fossils from the lime- 



