NO. 2229. FOSSIL PLANTS FROM BOLIVIA— BERRY. 105 



Above 12,500 feet and extending to the snow line (about 17,500 

 feet) is the "puna brava," a bleak inhospitable region of shepherds 

 and miners, and with arctic rosette plants and a few grasses. 



POTOSI. 



Cerro Rico de Potosi or Potosi Mountain lies immediately south- 

 east of the town of Potosi in the northern part of the Province of 

 that name, in the eastern Andes or Cordillera Real, which forms the 

 eastern boundary of the high plateau of Bolivia. The mountain, 

 v/hich has a height of 15,381 feet, consists of a core of rhyolite sur- 

 rounded by conglomerates, shales, and tuffs. Fossil plants are abun- 

 dant in the latter on the northeast slope of the mountain and also 

 in some of the mine tunnels. 



Silver was discovered at Potosi in 1544, and mining for this metal 

 and latterly for tin has been in operation for over 350 years. An 

 account of the region has recently been published by Miller and Sin- 

 gewald,^ who collected the fossils that are the basis of the present 

 contribution. 



COROCORO. 



Corocoro is near the western edge of the high plateau (altiplanicie) 

 of Bolivia in a group of low structural hills such as not infrequently 

 project through the flat surficial deposits of the plateau. It lies a 

 short distance south of the Arica-La Paz Railroad in the Province 

 of La Paz, about 100 kilometers southwest of the town of La Paz 

 and at an altitude of slightly more than 13,000 feet. It is about 

 2° north and 2° 40' west of Potosi. The country rock is a thick and 

 much faulted series of prevailingly red, gypsiferous and ferruginous 

 shales, sandstones, and conglomerates. Copper has been mined at 

 Corocoro since before the arrival of the Spaniards in the sixteenth 

 century, and a general account of the district has recently been pub- 

 lished by Singewald and Miller. ^ 



AGE OF THE COROCORO ROCK. 



Opinions regarding the age of this series have ranged from Carbo- 

 niferous to Tertiary. These have not been based upon paleonto- 

 logic evidence, hov/ever, since no fossils have hitherto been known 

 from the series. Messrs. Singewald and MiUer collected fossil plants 

 from a sandy tuff northwest of Corocoro and obtained the cast of a 

 footprint from a specimen collected by Fernando Dorian, manager of 

 the Corocoro Copper Mines (Ltd.) along the raiboad between Tarejra 



1 Miller and Singewald, Mining Conditions at Potosi, Bolivia. Eng. and Min. Journ., vol. 103, 1917, 

 pp. 255-200. 



2 Singewald and Miller, The Corocoro Copper District of Bolivia, Eng. and Min. Journ., vol. 103, 1917, 

 pp. 171-176. 



