156 TERTIARY ROCKS OF AUSTRALASIA, 



teristics in the assemblages of the mollusca, the New- 

 Zealand rocks do not present to the classifier such difficulties 

 as those referred to with respect to the members of the 

 system in Austraha and Tasmania, — where, with the 

 exception, perhaps, of a limited patch of marine beds of 

 later age at Flemington, Victoria, the whole of the marine 

 formations are confined to an extensive though continuous 

 series of formations, which, if we trust to the percentage 

 method, must be restricted to the earUest Tertiary period 

 (probably Eocene). 



None of the various bands or groups in Australia and 

 Tasmania contain more than from about 1 to 5 per cent, 

 of species of molluscs having living representatives. It 

 is significant, too, that as the molluscs of these beds are 

 more thoroughly investigated the tendency is to reduce 

 even this very small percentage. Whatever advantage 

 there may be locally in distinguishing certain zones within 

 the Australian and Tasmanian series, it seems, therefore, 

 almost certain, according to the percentage method, that 

 they should be classed as Eocene rather than Ohgocene 

 or Miocene, to which periods some of the divisions have 

 been referred by some authorities. 



With such advantages as those referred to, the New 

 Zealand geologists have greater facilities for determining 

 the position of their numerous lacustrine formations con- 

 taining lignites, coals, and other vegetable drifts. 



From the fact that some of the marine formations of 

 the Pareora system are now found at an altitude of over 

 2000 feet above sea level, it is evident that New Zealand 

 has been subjected to even greater physical changes than 

 Australia and Tasmania since the early Tertiary period. 

 The greater extent of glaciation in the Neogene epoch in 

 New Zealand is also evidently isochronous with the sup- 

 posed colder epoch in Austraha and Tasmania, and it is 

 generally regarded by the geologists of New Zealand as 

 mainly due to the very much greater elevation of the land 

 at that time. 



Life of the Period in Australia and Tasmania, 



The following tables show the probable distribution, in 

 time, of the genera of plants and molluscs occurring in 

 Australia and Tasmania during the Tertiary period, 



