512 EIGENMANN— ORIGIN OF FISHES OF THE 



the Andes are difficult questions, especially in view of the fact that 

 the principal territory at present occupied by the Esmeraldas- 

 Guayas systems is quaternary and the Andes are, in part at least, 

 tertiary, and are everywhere, east of the Guayas, far above the 

 habitat of the genera whose origin is sought. Evidently the Guayas 

 is simply the present gathering place of the Pacific slope fauna 

 of Ecuador, not necessarily the original western habitat of these 

 fishes. 



In this connection the discovery of Berry is of interest {Proc. 

 U. S. Nat. Mils., LIV., p. 114) 



" that the fossil flora found in the tufifs at Potosi is very similar to existing 

 assemblages found in eastern Bolivia or at various other places in the 

 Amazon basin," 



and that 



" From a consideration of all the evidence available it is concluded that 

 the flora is Pliocene in 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." 



Of even greater interest is Berry's discovery {Proc. U. S. Nat. 

 Mus., LV.) that the fossil plants taken, p. 279, 



" from a clay lens overlying a bed of lignite in the petroleum-bearing sands 

 about 20 miles south of the town and river of Tumbez and 200 or 300 

 feet inland from the shore of the Pacific," p. 283, " furnish convincing evi- 

 dence that the coastal region of Peru during the early Miocene was a region 

 covered with a dense tropical forest, including a variety of broad-leaved 

 mesophytic hardwoods mixed with lianas and large feather palms, and that 

 the climate and rainfall were in striking contrast with what they are at 

 the present time in this region. This would seem to indicate that in the 

 early Miocene the Ecuadorian and Peruvian Andes had not yet inter- 

 posed their height in the path of the easterly moisture-bearing trade winds 

 and that the present coastal desert was not in existence." 



This discovery shows that what is now the Pacific slope was 

 habitable for fresh-water fishes in comparatively early time, before 

 the Andes were the formidable barrier they now present. It is quite 

 within reason, therefore, that the present fish-fauna of the Guayas 

 did not come from the east across a barrier but that at a time pre- 

 ceding the origin of the present species a section of a continuous 

 fauna was segregated from the rest by the formation of the 

 mountainous screen between them. 



