ion had been accomplished,
the heat must have been comparatively uniform in all latitudes; but,
that point gained, there necessarily ensued an arrangement of zones of
different temperatures, or, in other words, climates appeared, the
process being essentially slow, and becoming slower as the loss of heat
went on. Finally, when loss of heat from the earth ceased, an
equilibrium was reached in the climate arrangement as we now find it.
Thus purely physical as well as geological considerations brought
philosophers on this point to the same conclusion--that conclusion which
has been so often repeated--very long periods of time.

[Sidenote: Consequent effect on the Flora and Fauna.] 2nd. As to the
effect on the organic world. Nothing can live at a temperature higher
than the boiling-point of water, for the condition of life implies that
there shall circulate from part to part of a living mechanism a watery
liquid, sap, or blood. From this it necessarily follows that a planet,
the temperature of which is above a certain limit, must necessarily have
a lifeless surface; and this seemed to be the interpretation of that
pre-organic time to which we have referred. Moreover, when the
temperature suitably descends so as to come within the limit at which
life is possible, its uniformity over the surface of a planet will
produce a sameness in the organization. It would be an identity if heat
were the only regulating condition of life. At this stage of things, the
solar heat being overpowered, and a sensibly uniform temperature in all
latitudes existing, still the only possible organic forms are those
consistent with a high temperature, uniformity in the physical condition
impressing a general uniformity in the aspect of life geographically.
[Sidenote: Production and distribution of new organisms.] But the moment
that climate arrangement has become possible, variety of organic form
becomes possible. Now also ensues another all-important
result--geographical distribution. Both of plants and animals, those
whose vital conditions are inconsistent with the occurring change must
retire from the affected locality. In plants this retrocession is
brought to pass by the gradual sickening and death of individuals, or
the impossibility of reproduction; in animals there is added thereto,
because of their power of locomotion, voluntary retirement, at least in
the case of individuals, and immobility in the species is corrected by
locomotion in the i