COROCORO COPPER DISTRICT OF BOLIVIA 51 



Tarejra, and at other points in the vicinity. In 1915, Mr. 

 Fernando Dorion, general manager of the Corocoro Copper 

 Mines, Ltd., gave Singewald and Miller a plaster cast of a 

 fossil footprint found in a small quarry along the railroad 

 about 3 km. southwest of Corocoro. The stratigraphic 

 relations of the beds at this locality to the Vetas and Ramos 

 were then unknown. The plaster cast was examined by 

 Professor Richard S. Lull who thought it represented the 

 foot print of a form closely related to Cheirotherium and 

 hence of Triassic age. In 1919, Mr. Dorion gave the authors 

 the original specimen. A further examination of it leads to 

 the conclusion that it probably represents an Edentate or 

 sloth, possibly related to some such form as Priodontes, but 

 as yet of undetermined affinities. It cannot be older than 

 Pliocene and may be Pleistocene in age. This determination 

 is thoroughly in harmony with the stratigraphic position of 

 the series as determined by its structural relations. 



The Desaguadero series is, therefore, younger than the 

 Vetas and Ramos and of Pliocene or Pleistocene age. 



The Desaguadero series is believed to correspond in a 

 general way with what Pompeckj (1905) called the Puna 

 beds. The source of materials was largely from the older 

 Ramos rocks in the immediate vicinity augumented by 

 volcanic materials from the Western Range. It seems 

 probable that the Desaguadero series was at least partially 

 synchronous with much of the surficial deposits that mantle 

 the high plateau and through which the La Paz River has 

 cut back its valley. The mammal-bearing beds at Ulloma to 

 the south and the plant-bearing tuffs at Jancocata to the 

 north, we regard as of this age, although there is no direct 

 evidence for this conclusion. What appears to be the con- 

 tinuation of the Desaguadero series west of Corocoro ante- 

 dates the stream terraces along the Pontezuelo and 

 Desaguadero rivers. 



The borings and sun cracks in the rocks of this series 

 would suggest a seasonal rainfall. The conclusion to be 

 derived from the mammal fauna at Ulloma and the flora at 



