130 THK UCCURKENCK OK (UCANTlr MAKStlM ALS IN TASMANIA. 



simultaneous occurrence of higher organised mammals, 

 which have become extinct, and lower organised mollusca, 

 which are still nourishing, is of the greatest theoretical 

 importance. It proves conclusively that lower organised 

 animals are much less suscej. table to changes than higher 

 organised ones. The Ipwer oiganism is, apparently, better 

 fitted to adapt itself to changes than the higher one ; 

 changes which resulted in the complete disappearance 

 of the gigantic marsupials had not the slightest effect on 

 the molluscs. On the other hand, this simultaneous occur- 

 rence of extinct mammals and living molluscs conclusively 

 proves that in determining the age of certain beds from 

 fossils alone, we must be strictly guided by one class only. 

 It has been proved over and over again that the results as 

 to the age of certain beds derived from the study of, say, 

 the cchinodenns, are somewhat at variance with those de- 

 rived from the study of molluscs ; and, again, those derived 

 from the study of pelecypoda and gastropoda differ from 

 those obtained from the study of cephalopoda. Generally, 

 the lower classes are indicative of a somewhat older age 

 than the higher classes, because they are more persistent 

 than the latter. 



The j^resent land and fresh-water molluscan fauna 

 must, therefore, have already been in ex'str^nce when the 

 gigantic marsupials roamed over the Australian Continent, 

 and when Tasmania was still connected with the mainland. 

 It would, however, bo completely wrong to argue that it 

 must bo of great age, becavise these giants have since died 

 out. 



Stratigraphically, the beds in the Mowbrav Swamp are 

 also of very recent age; in fact, thev were formed when the 

 present physiographical features of Tasmania had been 

 practically formed, except that in all probability th? eleva- 

 tion of the swam]) above sea level was then higher than it is 

 now. 



It almost seems significant that the remains of the 

 gigantic marsupials were discovered in such a part of Ta.s- 

 mania that probably was connected longer with the main- 

 land than others, but this is, perhaps, merely accidental. 

 For the present we are unable to say whether the gigantic 

 marsupials had a wider distribution in Tasmania, or 

 whether thev were restricted to the northern part. So far 

 no remains have been found at other localities, and R. M. 

 Johnston, the indefatigable geological explorer of Tasmania, 

 v»ould have most probablv discovered them had they 

 existed. However, this does not prove that they do not 



