me. The features of dispersal, intended to be explained by it, would
be accomplished just as well by an unknown number of islands which have
joined into larger complexes while elsewhere they subsided again:
like pontoon-bridges which may be opened anywhere, or like a series
of superimposed dissolving views of land and sea-scapes. Hence the
reconstructed maps of Europe, the only continent tolerably known, show
a considerable number of islands in puzzling changes, while elsewhere,
e.g. in Asia, we have to be satisfied with sweeping generalisations.

At present about half-a-dozen big connections are engaging our
attention, leaving as comparatively settled the extent and the duration
of such minor "bridges" as that between Africa and Madagascar, Tasmania
and Australia, the Antilles and Central America, Europe and North
Africa. (Not a few of those who are fascinated by, and satisfied with,
the statistical aspect of distribution still have a strong dislike to
the use of "bridges" if these lead over deep seas, and they get
over present discontinuous occurrences by a former "universal or
sub-universal distribution" of their groups.) This is indeed an easy
method of cutting the knot, but in reality they shunt the question only
a stage or two back, never troubling to explain how their groups managed
to attain to that sub-universal range; or do they still suppose that the
whole world was originally one paradise where everything lived side by
side, until sin and strife and glacial epochs left nothing but scattered
survivors?

The permanence of the great ocean-basins had become a dogma since it
was found that a universal elevation of the land to the extent of 100
fathoms would produce but little changes, and when it was shown that
even the 1000 fathom-line followed the great masses of land rather
closely, and still leaving the great basins (although transgression
of the sea to the same extent would change the map of the world beyond
recognition), by general consent one mile was allowed as the utmost
speculative limit of subsidence. Naturally two or three miles, the
average depth of the oceans, seems enormous, and yet such a difference
in level is as nothing in comparison with the size of the Earth. On
a clay model globe ten feet in diameter an ocean bed three miles deep
would scarcely be detected, and the highest mountains would be smaller
than the unavoidable grains in the glazed surface of our model. There
are but few countries w