here else, will be found a complete justification
of that lengthy investigation of the exact nature of past changes of
climate, which to some readers may have seemed unnecessary and unsuited to
such a work as the present. Without the clear and definite conclusions
arrived at by that discussion, and those equally important views as to the
permanence of the great features of the earth's surface, and the wonderful
dispersive powers of plants which have been so frequently brought before us
in our studies of insular floras, I should not have ventured to attack the
wide and difficult problem of the northern element in southern floras.

In concluding a work dealing with subjects which have occupied my attention
for many years, I trust that the reader who has followed me throughout will
be imbued with the conviction that ever presses upon myself, of the
complete interdependence of organic and inorganic nature. Not only does the
marvellous structure of each organised being involve the whole past history
of the earth, but such apparently unimportant facts as the presence of
certain types of plants or animals in one island rather than in another,
are now shown to be dependent on the long series of past geological
changes--on those marvellous astronomical revolutions which cause a
periodic variation of terrestrial climates--on the apparently fortuitous
action of storms and currents in the conveyance of germs--and on the
endlessly varied actions and reactions of organised beings on each other.
And although these various causes are far too complex in their combined
action to enable us to follow them out in the case of any one species, yet
their broad results are clearly recognisable; and we are thus encouraged to
study more completely every detail and {545} every anomaly in the
distribution of living things, in the firm conviction that by so doing we
shall obtain a fuller and clearer insight into the course of nature, and
with increased confidence that the "mighty maze" of Being we see everywhere
around us is "not without a plan."

{549}

INDEX

A.
Acacia, wide range of in Australia, 185
_Acacia heterophylla_, and _Acacia koa_, 443
Acaena in California, 527
_Accipiter hawaii_, 314
Achatinellinae, average range of, 317
_Aegialitis sanctae-helenae_, 305
Africa, characteristic mammalia of, 416
former isolation of, 418
Africa and Madagascar, relations of, 418
early history of, 419