150 STUDIES IN GEOLOGY, No. 4 



in lesser proportions is present in the so-called clay. Traces 

 of vegetation, aside from the layers of lignite with sticks 

 and branches, are present throughout the section in so far 

 as it was exposed, but the collected material came almost 

 entirely from stratums No. 2 and No. 4. 



In the former the leaves are imbedded at all angles and 

 degrees of curvature, and were evidently covered by wind 

 blown volcanic ashes when still dry and curled. In the latter 

 the percentage of volcanic ashes is much smaller, the leaves 

 are matted in layers parallel to the bedding planes, and the 

 material is laminated and obviously water laid, in the quiet 

 waters of what was either a permanent or seasonal lake. 

 After an analysis of the flora I will have something to say 

 regarding the climate and other physical conditions. 



Regarding the source of the volcanic ashes it may be noted 

 that the Eastern Andes offer a striking contrast to the 

 Western Andes. I know of no volcanic peaks, or effusive, 

 or fragmental igneous rocks in the Eastern Andes of Bolivia. 

 The v Western Andes on the other hand constitute one of the 

 most impressive volcanic regions of the world throughout 

 almost their whole extent, and the Mesozoic sediments which 

 enter so largely into their composition, are almost thoroughly 

 masked by tuffs, ash beds, and lava flows. Many of the 

 cones have only recently become extinct and many others are 

 still feebly active. It seems conclusive that the ash beds 

 found in the Eastern Andes at this and other localities in 

 Bolivia came from eruptions in the Western range, where 

 the nearest volcanoes to Pisllypampa are 250 miles to the west 

 of that place. 



THE FLORA AND ITS ENVIRONMENTAL CONDITIONS 



The distribution of land and water during the late Ter- 

 tiary could not have been sufficiently divergent from the 

 present geographic pattern to have altered the atmospheric 

 circulation, which, if it is different today in this region, as 

 seems improbable, is the result of orogenesis. The ashes 



