Balu in Borneo. Again, on the
summit of the Organ mountains in Brazil there are species allied to
those of the Andes, but not found in the intervening lowlands.

_No Proof of Recent Lower Temperature in the Tropics._

Now all these facts, and numerous others of like character, were
supposed by Mr. Darwin to be due to a lowering of temperature during
glacial epochs, which allowed these temperate forms to migrate across
the intervening tropical lowlands. But any such change within the epoch
of existing species is almost inconceivable. In the first place, it
would necessitate the extinction of much of the tropical flora (and with
it of the insect life), because without such extinction alpine
herbaceous plants could certainly never spread over tropical forest
lowlands; and, in the next place, there is not a particle of direct
evidence that any such lowering of temperature in inter-tropical
lowlands ever took place. The only alleged evidence of the kind is that
adduced by the late Professor Agassiz and Mr. Hartt; but I am informed
by my friend, Mr. J.C. Branner (now State Geologist of Arkansas, U.S.),
who succeeded Mr. Hartt, and spent several years completing the
geological survey of Brazil, that the supposed moraines and glaciated
granite rocks near Rio Janeiro and elsewhere, as well as the so-called
boulder-clay of the same region, are entirely explicable as the results
of sub-aerial denudation and weathering, and that there is no proof
whatever of glaciation in any part of Brazil.

_Lower Temperature not needed to Explain the Facts._

But any such vast physical change as that suggested by Darwin, involving
as it does such tremendous issues as regards its effects on the tropical
fauna and flora of the whole world, is really quite uncalled for,
because the facts to be explained are of the same essential nature as
those presented by remote oceanic islands, between which and the nearest
continents no temperate land connection is postulated. In proportion to
their limited area and extreme isolation, the Azores, St. Helena, the
Galapagos, and the Sandwich Islands, each possess a fairly rich--the
last a very rich--indigenous flora; and the means which sufficed to
stock them with a great variety of plants would probably suffice to
transmit others from mountain-top to mountain-top in various parts of
the globe. In the case of the Azores, we have large numbers of species
identical with those of Europe, and others closely a