PlSUvYPAMPA BOLIVIA 151 



that came to rest at Pisllypampa need not have come from 

 the nearest volcano but may have come from the Chilean 

 volcanoes if the winds were southwesterly or from the Peru- 

 vian volcanoes if they were northwesterly. These winds 

 would presumably be dry winds on reaching the Cochabam- 

 ba region since I should say that some sort of a divide ante- 

 dates the time of deposition of these deposits, and the mois- 

 ture bearing winds were the easterly trades as they are at 

 the present time. 



Hence Pisllypampa was, in Pliocene time, a region with a 

 wet summer and a less wet but not cold winter season, the 

 former extending approximately from September to May. 

 That the ash beds alternating with the lignite seams do not 

 indicate consecutive seasons is shown by the thickness of the 

 lignite which could scarcely have accumulated during a 

 single summer. I regard the deposit as one of many years 

 growth, the wind-blown ash beds indicating volcanic erup- 

 tions in the Western or Chilean Andes at intervals and when 

 the prevailing winds were favorable for transportation to 

 Pisllypampa. The ash in the waterlaid materials is easily 

 explained by reworking during which it was more or less 

 masked by silt and vegetable debris. It seems obvious also 

 that there were no high peaks in the vicinity at this time in 

 the Pliocene, but that the topography was one of maturity, 

 otherwise there would be some trace of pebbles or gravel or 

 sandstone, or resistant rock minerals, all traces of which 

 appear to be entirely absent. 



Our knowledge of the existing flora of Bolivia east of the 

 Andes and in the sub-andean ranges is very incomplete. 

 d'Orbigriy's Voyage dans 1'Amerique Meridionale contains 

 many botanical observations and there is the Flora Crucena 

 published by Pefia at Sucre in 1901. Weddell described 

 many plants from this region as a result of his Cinchona 

 studies during the first half of the nineteenth century, and 

 the enumeration of the Rusby and Bang collections resulted 

 in extensive lists of species. 



