rera on the Igaraparana River. Yapoboda, part of this 
broken range, is of special interest because, in the vast 
and sparsely explored Comisaria del Vaupés, it is located 
about midway between the westernmost mountains in 
the Apaporis and the Duida mass in Venezuela. 
In many other localities in Amazonian Colombia, one 
finds distant and very indistinct outliers of this ancient 
formation in the form of small areas of white sand with 
a low caatinga-forest or savanna vegetation. So indistinct 
topographically are some of these formations that it 
might be difficult geologically to identify them with the 
ancient Venezuela-Guiana land-mass were it not for the 
fact that their flora is so strikingly different from that of 
the surrounding Amazon jungle and so similar to that 
of a number of analogous areas in southern Venezuela 
and in the Guianas. It can be shown that these isolated 
patches have an ancient remnant flora which is most 
closely allied to the flora of the Duida-Roraima ranges 
and of other peaks in the same far-distant mountains on 
the northern rim of the Amazon Valley. 
As an example of these indistinct outliers, we may 
cite the rather extensive caatinga-forest between the 
headwaters of the Hamacayacu and Cotuhé Rivers in the 
interior of the trapécio amazénico (near Leticia). Similar 
areas occur near Mishuyacu and at Iquitos in Peru and 
at Sao Paulo de Olivenga on the upper Amazon River 
in Brazil. 
It is, therefore, apparent that a thorough study of the 
floras of these isolated mountains in eastern Colombia is 
of the utmost importance for a complete understanding 
of the origin and composition of the flora, not only of the 
Amazonas of Colombia, but also of large sectors of south- 
ern Venezuela, the Guianas and northern Amazonian 
Brazil. There would seem, likewise, to be some connec- 
tion between this ancient flora rimming the north of the 
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