CHAP. XXIII ARCTIC PLANTS IN NEW ZEALAND 529 



Conchcding Remarks 07i the Last Two Chapters, — Our 

 inquiry into the external relations and probable origin of 

 the fauna and flora of New Zealand, has thus led us on to 

 a general theory as to the cause of the peculiar biological 

 relations between the northern and the southern hemi- 

 spheres; and no better or more typical example could 

 be found of the wide range and great interest of the 

 study of the geographical distribution of animals and 

 plants. 



The solution which has here been given of one of the 

 most difficult of this class of problems, has been rendered 

 possible solely by the knowledge very recently obtained 

 of the form of the sea-bottom in the southern ocean, and 

 of the geological structure of the great Australian continent. 

 Without this knowledge we should have nothing but a 

 series of guesses or probabilities on which to found our 

 hypothetical explanation, which we have now been able 

 to build up on a solid foundation of fact. The complete 

 separation of East from West Australia during a portion of- 

 the Cretaceous and Tertiary periods, could never have been 

 guessed till it was established by the laborious explorations 

 of the Australian geologists ; ^ while the hypothesis of a 

 comparatively shallow sea, uniting New Zealand by a long 

 route with tropical Australia, while a profoundly deep 

 ocean always separated it from temperate Australia, would 

 have been rejected as too improbable a supposition for the 

 foundation of even the most enticing theory. Yet it is 

 mainly by means of these two facts, that we are enabled 

 to give an adequate explanation of the strange anomalies 



^ Mr. Spencer Moore (in his articles on tlie ** Origin of the Australian 

 Flora" in Natural Science^ Sept. and Oct. 1899) denies this, on the 

 ground that Tertiary deposits are not known to extend far inland. But 

 according to the best geological map of Australia (see Stanford's Com- 

 pendium, YoL I, p. 83), Tertiary formations surround the mountains of 

 Central Australia for six hundred miles from north to south, and, with 

 but moderate intervening Cretaceous areas (from above which they may 

 well have been removed by denudation as the chalk, and the eocene 

 from above the chalk, have been removed from above the wealden formation 

 in the South of England) distinctly indicate an extensive submersion such 

 as I suggest. Mr. Moore speaks pf " the palpable errors" of my views as 

 here expressed, but I cannot find that he has specified them ; and I may 

 now state, that, after again carefully reading his articles, I can find no 

 reason for modifying either the facts or the reasoning of the explanation 

 here given. 



