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Show 80 ISLAND LIFE. (rART I. Antiquity of Plants as affecting thei1· Distribution.-We have already referred to the importance of great antiquity in enabling us to account for the wide dispersal of some genera and species of insects and land-shells, and recent discoveries in fossil botany show that this cause has also had great influence in the case of plants. Rich floras have been discovered in the Miocene, the Eocene, and the Upper Cretaceous formations, and these consist almost wholly of living genera, and ma,ny of them of species very closely allied to existing forms. We Lave therefore every reason to believe that a large number of our plant-species have survived great geological, geographical, and climatal changes; and this fact, combined with the varied and wonderful powers of dispersal many of them possess, renders it far less difficult to understand the examples of wide distribution of the genera and species of plants than in the case of similar instances among animals. This subject will be further alluded to when discussing the origin of the New Zealand flora, in Chapter XXII. CHAPTER VI. GEOGRAPHICAL AND GEOLOGICAL CHANGES : THE "PERMANENCE OF CONTINENTS. Changes of Land and Sea, their nature and extent-Shore-deposits and stratified Rocks-The Movements of Continents- Supposed Oceanic formations; the Origin of Chalk-Fresh-water and Shore-deposits as proving the permanence of Continents-Oceanic Islands as indications of the permanence of Continents and Oceans- General stability of Continents with constant change of form-Effect of Continental Changes on the Distribution of Anim~ls-Changed distribution proved by the extinct Animals of different epochs-Summary of evidence for the general permanence of Continents and Oceans. THE changes of land and sea which have occurred in particular cases will be described when we discuss the origin and relations of the faunas of the different classes of islands. We have here only to consider the general character and extent of such changes, and to correct some erroneous ideas which are prevalent on the subject. Changes of Land and Sea, their nature and extent.-It is a very common belief that geological evidence proves a complete change of land and sea to have taken place over and over again. Every foot of dry land has undoubtedly, at one time or other, formed part of a sea-bottom, and we can hardly exclude the surfaces occupied by volcanic and fresh-water deposits, since, in many cases, if not in all, these rest upon a substratum of marine formations. At first sight, therefore, it seems a necessary inference that when the present continents were under water there must have been other continents situated where we now G |
