24 
ORIGIN OF THE ANDES 
cordance of from 4,000 to 5,000 feet in the east and west pro¬ 
jection of the valley floors in the Peruvian Andes.^'^ 
(6.) Seismic and volcanic evidences seem conclusive. 
(7.) Since the biologic evidence is likely to be somewhat un¬ 
familiar to most geologists, some space may be devoted to it. 
Floral and faunal criteria are available only north of latitude 5° S. 
The fresh-water fish fauna of the Guayas basin of Ecuador 
exhibits so close an affinity with that of Amazon that Scharf 
concludes any elevation must have been comparatively recent and 
this is confirmed by Henn and by the more detailed studies of 
Eigenmann.^^ 
According to T. Wolf,^® the flora is like that of the Choco 
(littoral of Colombia) and Panama and the Amazon part of 
Ecuador. Chapman states that the avifauna fully confirms the 
other biologic evidence, and that this was the latest passage for 
tropical species to be closed. 
The distribution of the existing flora and fauna in Colombia, 
so far as one can judge, appears to be entirely conditioned on 
topographic features of so recent a date of origin that sufficient 
time has not elapsed to permit of any considerable differentiation 
between those of the upper Orinoco and Amazon basins, the inter- 
Andean valleys, and the Pacific coastal region. No features can 
be correlated with any earlier montane topography. Chapman in 
his very excellent account of the Birds of Colombia (op. cit.) 
concludes that the bird-life of the Pacific Coast of Colombia and 
Ecuador is largely a pre-Andean fauna which was continuous 
with that of the Upper Amazon region, until cut off by the Andean 
uplift; that of the Cauca valley he regards as post-Andean. This 
uplift was so recent that sufficient time has not elapsed for 
differentiation on the two sides to have advanced as far or beyond 
the point where anything more than subspecies can be recognized. 
Wide ranging forms are disregarded so that the conclusions 
reached are entirely valid. 
14 In The Andes of Southern Peru, 1916, I. Bowman, gives an excellent summary 
of the physiographic proof of recent great uplift. 
15 Dist. and Origin of Life in America, p. 360, 1912. 
16 Science, N. S., Vol. XL, p. 603, 1914. 
17 Indiana University Biological Studies. 
18 Geographia y Geologia del Ecuador, p. 439. 
18 Bull. American Mus. Hist., Vol. XXXVI, p. 110, 1917. 
