the accumulation
of spores and sporangia on dry land. But if we consider the matter
more closely, I think that this apparent objection loses its force. It
is clear that, during the Carboniferous epoch, the vast area of land
which is now covered by Coal-measures must have been undergoing a
gradual depression. The dry land thus depressed must, therefore, have
existed, as such, before the Carboniferous epoch--in other words, in
Devonian times--and its terrestrial population may never have been
other than such as existed during the Devonian, or some previous
epoch, although much higher forms may have been developed elsewhere.

Again, let me say that I am making no gratuitous assumption of
inconceivable changes. It is clear that the enormous area of Polynesia
is, on the whole, an area over which depression has taken place to
an immense extent; consequently a great continent, or assemblage of
subcontinental masses of land, must have existed at some former time,
and that at a recent period, geologically speaking, in the area of
the Pacific. But if that continent had contained Mammals, some of
them must have remained to tell the tale; and as it is well known that
these islands have no indigenous _Mammalia_, it is safe to assume that
none existed. Thus, midway between Australia and South America, each
of which possesses an abundant and diversified mammalian fauna, a mass
of land, which may have been as large as both put together, must have
existed without a mammalian inhabitant. Suppose that the shores of
this great land were fringed, as those of tropical Australia are now,
with belts of mangroves, which would extend landwards on the one
side, and be buried beneath littoral deposits on the other side,
as depression went on; and great beds of mangrove lignite might
accumulate over the sinking land. Let upheaval of the whole now take
place, in such a manner as to bring the emerging land into continuity
with the South-American or Australian continent, and, in course of
time, it would be peopled by an extension of the fauna of one of these
two regions--just as I imagine the European Permian dry land to have
been peopled.

I see nothing whatever against the supposition that distributional
provinces of terrestrial life existed in the Devonian epoch, inasmuch
as M. Barrande has proved that they existed much earlier. I am aware
of no reason for doubting that, as regards the grades of terrestrial
life contained in them, one of these m