372 PROCEEDINGS OF SECTION E. 



there are no apparent proofs of a continuity of land surface 

 uniting Tasmania to Australia proper during Tertiary times, 

 yet a comparison of the sequence of the great rock-masses in 

 l)oth areas would certainly suggest that Tasmania forms part of 

 the Australian continent geologically. With reference to the 

 date of the introduction of the present endemic alpine species, 

 this may be safely centred in the glacial movements which 

 T think, took place in the Southern Hemisphere during Post- 

 Miocene times. By the light which these glacial movements 

 throw upon the subject, it is not difficult to understand how a 

 tropical flora, extending during Miocene, or even early Pliocene 

 times throughout Eastern Australia, was gradually replaced by 

 the present remnants of an Antarctic flora at the higher eleva- 

 tions, and the mixed forms which prevail at sub-alpine habitats. 

 During the refrigeration which culminated in a glacial period, 

 those tropical forms which were able to accommodate themselves to 

 the decreasing temperature, might survive as stunted varieties, 

 which have differentiated under the changing climatic conditions, 

 while a large number of genera and species unable to withstand 

 the intense cold, would doubtless perish. 



The immigration and dissemination of antarctic types would, 

 in all probability, increase in proportion to the extinction of many 

 of the tropical types ; and it is at least conceivable that com- 

 minglingof species took place, andthecross fertilisation of an altered 

 tropical with an antarctic species produced forms able to with- 

 .stand greater extremes of temperature, and that prolonged periods of 

 slowly changing climatic conditions might result in the differentia- 

 tion of varieties so distinct from the original species, as to claim 

 true specific rank. 



The breaking up of the glaciers, and the gradual raising of 

 temperature to the present time, with the varying oscillations of 

 land-surface by sub-aerial denudation affecting difl'erent geological 

 formations in respect to ratios of denudation and erosion, &c., 

 might also produce analagous effects, as, by immigration, the 

 tropical, or extra-tropical forms began to commingle with, or re- 

 place, the antarctic forms in the lowlands, until the latter became 

 restricted to the higher elevations, where they now occur. The 

 presence of many extra-tropical northern species is, no doubt, 

 peculiar, although, as remarked by 8ir J. W. Hooker, " if as 

 complete evidence of such a proportionally cooled state of the 

 inter-tropical regions were forthcoming as there is of a glacial 

 condition of the temperate zones it would amply suffice to account 

 for the presence of European and arctic species in the antarctic." 

 Comparison with Tasmania. — Of the five hundred and eighty- 

 three species collected by the author, at elevations exceeding 

 2,000 feet, in the Australian Alps, not more than fifty-four are 

 truly endemic, while no less than eighty-nine are restricted to 

 Tasmania and the Australian Alps. 



