xxil 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 imist 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 inhabitf. 



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 J, and they receive addi- 



iinportant observations on Lis 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 iu 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 LyelFs 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 diffeY 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. 



f See the Principles of Geology, ed. 9. p. 702, and Address to the Geological Society of London by the Presi- 

 dent (Leonard Homer, Esq.), in 1847, p. 66. 



J 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 



