PUOCENE PISLLYPAMPA BOLIVIA 155 



The flora itself, in its close relationship with that still exist- 

 ing at lower and more humid levels in the same general 

 region, also points to a relatively modern age. 



There are three known Pliocene floras in Bolivia for com- 

 parison. These are the partially described floras found at 

 Potosi and at Corocoro, 2 and a third of limited extent and 

 described in the following contribution. Earlier South 

 American fossil floras are those from the Miocene of Chile, 3 

 Peru, 4 Ecuador, 5 Colombia 5 and Venezuela. 6 



The last five floras just mentioned are of slight value since 

 all are considerably older than the Pisllypampa flora. The 

 most important for comparative purposes are those of Po- 

 tosi and Corocoro. The latter contain a large number of types 

 that are closely related to existing forms of the Amazon 

 Basin and montafia zone of the sub-andean slopes, more 

 particularly among the Leguminosse. They abound in forms 

 with compound leaves of small leaflets, and clearly denote 

 somewhat different climatic conditions from those indicated 

 by the Pisllypampa plants. In my preliminary account of 

 the Potosi and Corocoro floras my conclusions, which were 

 based. upon the extant botanical literature and before I had 

 seen the region, are subject to certain modifications resulting 

 from my field studies, and these will be fully discussed in a 

 separate contribution. 



The Potosi and Corocoro floras denote more arid, or at 

 least drier, conditions than does the Pisllypampa flora not 

 of course the aridity and cold of present day Potosi, but con- 



2 Berry, E W., Proc. U. S. Natl. Mus., vol. 54. pp. 103-164, pis. 

 15-18, 1917. 



3 Engelhardt, H., Abh. Senck. Naturf. Gesell., Bd. 16, pp. 629-692, 

 pis. 1-14, 1891. 



"Berry, E. W., Proc. U. S. Natl. Mus., vol. 55, pp. 2^9-294, pis. 

 14-17, 1919. 



5 Engelhardt, H., Abh. Senck. Naturf. Gesell., Bd. 19, pp. 1-47, 

 pis. 1-9, 1895. 



6 Berry, E. W., Proc. U. S. Natl. Mus., vol. 59, pp. 553~579, pis. 

 107-109, 1921. 



