38 STUDIES IN GEOLOGY, No. i 



stones at Miraflores, a locality in the eastern Andes, 365 km. 

 southeast of Corocoro. The authors likewise collected 

 Cretaceous forms from these limestones at Miraflores and at 



other localities between Miraflores and Potosi and can sub- 



t 



stantiate Steinmann on this point. Both his description 

 and age determinations of the Puca sandstone apply to the 

 red rocks of the eastern range of the Bolivian Andes, but 

 they do not apply to the Corocoro rocks. He states further 

 that at the end of the Pliocene and in Quaternary thin red 

 sandstones were again deposited as continental deposits out 

 of the Puca sandstone and hence are similar to it in com- 

 position and color. And since the period of the close of the 

 Tertiary and the Quaternary is that of the injection of 

 granodiorites and flow of trachytic-dacitic rocks these 

 younger red sandstones contain fragments, tuffs, and flows 

 of the younger eruptives. This answers the description of 

 the Corocoro rocks better than does that of the Puca sand- 

 stone and corresponds more nearly with their true age. The 

 Corocoro rocks are not the equivalent of the Puca sandstone 

 of the eastern Andes lithologically and are not of the same 

 age. 



Douglas (p. 28) because of the wide Cretaceous trans- 

 gression over the older rocks which he observed in Peru 

 where similar beds of red sandstone are occasionally inter- 

 bedded with limestone, concluded that the red sandstone 

 series of Bolivia might be regarded as a shallow-water 

 facies of the fossiliferous Cretaceous limestones of the 

 Peruvian sierras. 



Singewald and Miller describe the occurrence of a ledge 

 of plant-bearing sandstone in a gulch northwest of the city 

 that was called to their attention by Mr. Fernando Dorion 

 and from which they secured a collection of plants that were 

 determined by Berry as Pliocene. As the locality is in the 

 Vetas not far from the Corocoro fault, this flora fixes 

 definitely the age of the Vetas. 



In 1919 the authors examined the Corocoro rocks with 

 some care for additional paleontologic evidence and found 

 that the fossil plants occur at a number of horizons in the 



