164 STUDIES IN GEOLOGY, No. 4 



coriaceous texture, and with an entire margin except where 

 mechanically split. Indicated length about 33 cm. Maxi- 

 mum width, which is below -the middle of the leaf, about 7.5 

 cm. Midrib stout, circular in cross section, prominent on the 

 under side of the leaf. Venation of closely spaced, relatively 

 stout, simple laterals, which diverge from the midrib at 

 angles of about 75 to 80 degrees, and proceed with but 

 slight curvature to the lateral margins. Petiole presumably 

 long and stout. 



This well marked species is unfortunately represented by 

 a single specimen which was somewhat broken in transit. 

 It occurs in the water laid part of the section and obviously 

 represents a leaf of Heliconia the American wild banana. 

 The relationship is clear and I can see no reason for using 

 the generic term Musaphyllum, which latter is open to 

 objection in this connection since it indicates or at least 

 suggests an unwarranted degree of affinity to the existing 

 genus Musa which is not borne out by the geological history 

 of the family. 



This is another one of the species found fossil at this 

 locality that serves to ally this fossil flora with the existing 

 Yungas flora of eastern Bolivia. I did not penetrate far 

 enough toward the Amazon plain to observe the changes 

 in flora below elevations of 5,000 feet, nor are travellers' ac- 

 counts detailed enough to be of much value. The geologic 

 interest centers in the possible upper limits of the tropical 

 and sub-tropical forest. In the humid valley of the Rio 

 Undavi I found Heliconia associated with tree ferns, peppers, 

 gleichenias and giant cannas up to elevations of 7,000 feet. 

 Weberbauer gives 5,850 feet as the upper limit of Heliconia 

 in southern Peru, which is nearer the equator. This may be 

 an excessively low figure but on the other hand warm types, 

 for some unknown reason, appear to range to greater eleva- 

 tions in the Yungas than they do farther north. Heliconias 

 are commoner, however, at somewhat lower levels than those 

 cited above so that in the latitude of Pisllypampa one would 



