114 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.54. 



these Festuca, Escallonia, Polystichum, Porliera, and Ewphorbia are 

 represented outside the Andean region, leaving only Amicia and 

 Myrteola as typically Andean plants. Plants of extra-tropical cli- 

 matic requirements in that they are montane forms and hence live 

 under temperate temperatures or in arid situations include Festuca, 

 Escallonia, Amicia, Polystichum, Porliera, EupJiorhia, and Myrteola, 

 the same genera previously enumerated as Andean m character. 

 Polystichum and Escallonia are not certamly indicative of temperate 

 conditions nor is Euphorbia, although the latter as well as Porliera 

 indicate more or less aridity. It is not possible to determme what 

 the relation of these few forms is to the predominantly humid and 

 tropical character of the bulk of the Potosi flora. Possibly it is to be 

 explained by local aridity of sandy areas of soil under a tropical sun, 

 or there may have been elevations near to the basin of sedimentation 

 that would explain this element of the fossil flora. The absence of 

 large-leafed species in the flora as a whole and the vast predominance 

 of compound leaves with small leaflets, may also have been due to a 

 sandy substratum. 



While botanists may justly object to the reference of some of the 

 Potosi forms to one genus rather than another when several alterna- 

 tives are presented, and this comment is especially applicable to the 

 leaflets of the Legmninosae which are so abundant in the Potosi 

 deposits, none, I think, can oppose the conclusion that whatever the 

 opinion of students regarding the validity of some of the identifica- 

 tions, m no case does this uncertamty in any number of specific cases 

 alter the outstandmg result of this study, namely, that the fossil 

 flora found in the tuffs at Potosi is very similar to existmg assem- 

 blages found in eastern Bolivia or at various other places m the 

 Amazon Basin, or that the conditions of existence for the fossil flora 

 must have been similar to that mider which those existing floras with 

 which it has been compared are flourishing and quite different from 

 the environmental conditions prevailing at the present time withm 

 the eastern Andes of Bolivia or on the high plateau or in fact any- 

 where west of the region of heavy rains on the eastern slopes of the 

 front range. 



From a consideration of all the evidence available it is concluded 

 that the flora is Pliocene m age and that the major elevation of the 

 eastern Andes of Bolivia and the high plateau took place in the late 

 Pliocene and throughout the Pleistocene and that the extensive 

 mineralization of this region also took place during this same period. 



