XXII FLORA OF NEW ZEALAND. 
need not be denied; and the other, that such risings and sinkings are in active progress over 
large portions of the continents and islands of the southern hemisphere. It is to the works of 
Lyell* that I must refer for all the necessary data as to the influence of climate in directing the 
migration of plants and animals, and for the evidence of the changes of climate being dependent on 
geological change. In the ‘ Principles of Geology’ these laws are proved to be of universal appli- 
cation, and amply illustrated by their being applied to the elucidation of difficult problems in geogra- 
phical distribution. It follows from what is there shown, that a change in the relative positions of sea 
and land has occurred to such an extent since the creation of still existing species, that we have no 
right to assume that the plants and animals of two given areas, however isolated by ocean, may not 
have migrated over pre-existing land between them. This was illustrated by an examination of 
the natural history of Sicily (where land-shells, still existing in Italy, and which could not have 
crossed the Straits of Messina, are found imbedded on the flanks of Etna high above the sea-level), 
regarding which Sir Charles Lyell states that most of the plants and animals of that island are older 
than the mountains, plains, and rivers they now inhabitt. 
It was reserved for Professor Edward Forbes, one of the most accomplished naturalists of his 
day, to extend and enlarge these views, and to illustrate by their means the natural history of an 
extensive area; which he did by applying a profound knowledge of geology and natural history to 
the materials he had collected during his arduous surveys of many of the shores of Europe and the 
Mediterranean. The result has been the enunciation of a theory, from which it follows that the 
greater part, if not all, of the animals and plants of the British Islands have immigrated at dif- 
ferent periods, under very different climatic conditions; and that all have survived immense changes 
in the configuration of the land and seas of Northern Europe. The arguments which support 
this theory are based upon evidence derived from Zoology and Geology}, and they receive addi- 
important observations on his own islands. The fact of this accomplished Naturalist and Geologist having pre- 
ceded me in the investigation of the Natural History of the Southern Ocean, has materially influenced and greatly 
furthered my progress; and I feel it the more necessary to mention this here, because Mr. Darwin not only directed my 
earliest studies in the subjects of the distribution and variation of species, but has discussed with me all the argu- 
ments, and drawn my attention to many of the facts which I have endeavoured to illustrate in this Essay. I know 
of no other way in which I can acknowledge the extent of my obligation to him, than by adding that I should never 
have taken up the subject in its present form, but for the advantages I have derived from his friendship and 
encouragement. 
* To Sir Charles Lyell’s works, indeed, I am indebted for the enunciation of those principles that are essential 
to the progress of every naturalist and geologist; those, I mean, that affect the creation and extinction, dispersion 
and subsequent isolation of organic beings; and though botanists still differ in opinion as to the views he 
entertains on the most speculative of subjects (the origin and permanence of species), there is, I think, but one as 
to the soundness and originality of his observations on all that relates to the strict dependence of organic beings on 
physical conditions in the state of the earth’s surface. ` I feel that I cannot over-estimate the labours of this great 
philosopher, when I reflect that without them the science of geographical distribution would have been with me 
little beyond a tabulation of important facts; and that I am indebted to them, not only for having given a direction 
to my studies in this department, but for an example of admirable reasoning on the facts he has collected regarding 
the distribution of plants and animals. I have no hesitation in recommending- the * Principles of Geology’ to the 
New Zealand student of Nature, as the most important work he can study. 
+ See the Principles of Geology, ed. 9. p. 702, and Address to the Geological Society of London by the Presi- 
dent (Leonard Horner, Esg.), in 1847, p. 66. 
+ For the contents of the Essay itself, I must refer to the Records of the Geological Survey of Great Britain, 
vol. i. p. 336. This is the most original and able essay that has ever appeared on this subject, and though I cannot 
