is view cuts the Gordian knot
of the dispersal of the same species to the most distant points, and
removes many a difficulty: but to the best of my judgment we are not
authorized in admitting such enormous geographical changes within
the period of existing species. It seems to me that we have abundant
evidence of great oscillations of level in our continents; but not of
such vast changes in their position and extension, as to have united
them within the recent period to each other and to the several
intervening oceanic islands. I freely admit the former existence of many
islands, now buried beneath the sea, which may have served as halting
places for plants and for many animals during their migration. In the
coral-producing oceans such sunken islands are now marked, as I believe,
by rings of coral or atolls standing over them. Whenever it is fully
admitted, as I believe it will some day be, that each species has
proceeded from a single birthplace, and when in the course of time we
know something definite about the means of distribution, we shall be
enabled to speculate with security on the former extension of the land.
But I do not believe that it will ever be proved that within the recent
period continents which are now quite separate, have been continuously,
or almost continuously, united with each other, and with the many
existing oceanic islands. Several facts in distribution,--such as the
great difference in the marine faunas on the opposite sides of almost
every continent,--the close relation of the tertiary inhabitants of
several lands and even seas to their present inhabitants,--a certain
degree of relation (as we shall hereafter see) between the distribution
of mammals and the depth of the sea,--these and other such facts seem to
me opposed to the admission of such prodigious geographical revolutions
within the recent period, as are necessitated on the view advanced
by Forbes and admitted by his many followers. The nature and relative
proportions of the inhabitants of oceanic islands likewise seem to me
opposed to the belief of their former continuity with continents. Nor
does their almost universally volcanic composition favour the admission
that they are the wrecks of sunken continents;--if they had originally
existed as mountain-ranges on the land, some at least of the islands
would have been formed, like other mountain-summits, of granite,
metamorphic schists, old fossiliferous or other such rocks, instead of