36 STUDIES IN GEOLOGY, No. T 



in the Quimsa Cruz mine is mentioned (p. 47). The 

 determination of the post-Pliocene Macrauchenia boliviensis 

 by T. H. Huxley which was found in the Santa Rosa mine 

 did not shake Forbes' faith in the Permian age of the Coro- 

 coro rocks for he remarks (p. 47) that it "appears only to 

 be accounted for on the supposition that the animal had 

 fallen into a fissure in these rocks." 



Reck cites the presence of abundant plant impressions 

 along the bedding planes and of petrified wood impregnated 

 with copper and also of fossil bones that are petrified and 

 the interiors of which are filled with native copper, but does 

 not give determinations either of the forms or of their age. 

 On the other hand, he says: (p. 95) 



"I am indebted to the kindness of my friend Ph. Krober, who 

 lived a considerable time in Corocoro, for the opportunity of citing 

 the occurrence in the metalliferous beds of Tcrcbratula elongata, 

 Cyathocrinus ramosus, and Trotosaurus, and the complete absence 

 of fossils in the non-metalliferous beds." 



The fossils indicate Rothliegendes or Zechstein, that is, 

 Permian age. In view of our present knowledge of the 

 Corocoro rocks it is certain that these forms did not come 

 from them and that there is a mistake in the locality. 



Noggerath exhibited specimens from Corocoro showing 

 flattened plant stems impregnated with metallic copper but 

 made no use of them in his correlation of the rocks which, 

 because they are lithologically similar to the Rothligendes 

 and the Buntsandstein and because they are copper-bearing, 

 he considers certainly of Rothliegendes or Permian age. 



Mossbach was doubtless merely following his predecessors 

 in considering the Corocoro strata of Rothliegendes age. 

 To the west, along the banks of the Desaguadero River, he 

 says they are overlain by Triassic Buntsandstein beds. He 

 mentions the occurrence of native copper replacing conifer 

 wood in the Ramos and Vetas. (p. 96) 



L. Sundt recognized the lack of scientific basis for the 

 earlier correlations of the Corocoro rocks and arrived at 

 more nearly correct conclusions though by a rather pre- 



