2c8 STUDIES IN GEOLOGY, No. 4 



The fossil plants from Jancocata comprise but nine deter- 

 minable species, a much too limited number upon which to 

 base sweeping conclusions. They include a fern, a reed-like 

 grass, an alder, two aborescent Rosacese, three Leguminosae, 

 and a member of the family Melastomataceae. They thus 

 represent 9 genera, 7 families and 5 orders. Their exact 

 age is a matter of some doubt. All are closely related to 

 still existing species of South America found at the same 

 or lower levels. Consistent with the opinion expressed in a 

 preceding paragraph they may be called Pliocene, belonging 

 toward the close of that period. It should be borne in mind, 

 however, that there is no adequate evidence of a definite 

 Pleistocene period in South America which was coterminous 

 with the Pleistocene of the Northern Hemisphere, so that it 

 might perhaps be better to state the age of the Jancocata 

 plants as Plio-Pleistocene. 



Although this flora is so limited it is definite enough in the 

 evidence which it furnishes that it antedated the present cli- 

 matic cycle in Bolivia. About the only existing aborescent 

 forms in the Titicaca basin are the small scrubby wild-olive, 

 so-called (Buddleia, Loganacese) and the kefiua (Polylepis 

 racemosa), and it is obvious that these fossils indicate a 

 wetter climate than that of the present. This conclusion is 

 reinforced by the lack of similarities between the fossils and 

 the chaparral of the Chaco of eastern Bolivia where grow 

 such things as Aspidosperma, Acacia, Prosopis, Capparis, 

 etc. Every one of the allies of these fossil species occurs 

 under more humid conditions, the majority in the more hu- 

 mid valleys of the montana zone, although some are lowland 

 types. 



It may be considered established that at Jancocata in late 

 Pliocene time there was more humidity and a greater rain- 

 fall the abundance of grass fragments is a further confirm- 



