766 STUDY OF THE ODONATA OF TASMANIA, 



which the Pleistocene Period saw the rise and fall upon the main- 

 land." 



The late Mr. A. W. Howitt*, in an able discussion on the Tas- 

 manian aborigines, states: "In early Tertiary, or even late pre- 

 Tertiary times . . . the northern part of Tasmania was relatively 

 higher above sea-level by at least 270 feet than it is now." Later, 

 "a period of great basaltic extrusion covered and protected many of 

 the Older Tertiary Sediments, and culminated in a widespread sub- 

 sidence to some 1,000 feet on the west coast and 700 feet on the 

 north coast of Tasmania. . . . Subsequently there was a re-elevation 

 of the land during Pleiocene and more recent times. . . . The com- 

 mencement of this later connection of Tasmania and Victoria may 

 be provisionally placed in the Pleiocene epoch." He also gives a 

 map showing the 50 and 100 fathom lines for the depth of the sea 

 over the area in question, from which it can be seen that the eleva- 

 tion of 270 feet mentioned, would be quite sufficient to lay bare 

 nearly all that portion now known as Bass Straits. 



Mr. C. Hedleyf (1903), in a very interesting paper, shows that 

 the marine Molluscan fauna of the southern coast-line of Australia 

 is not continuous from east to west, but can be subdivided into two 

 very distinct faunas, the "Adelaidean" westwards and the "Pero- 

 nian" eastwards, each distinguished by the possession of many 

 special forms. Further, though the fauna of the east coast to Cape 

 Howe is Peronian, the fauna of Hobson's Bay and Westernport is 

 shown to be Adelaidean. The striking conclusion is drawn, that the 

 Bassian Isthmus must, therefore, have lasted much later, as a nar- 

 row connection between Wilson's Promontory and the North-East 

 of Tasmania, than it did as a connection with the north-west of the 

 island. Mr. Hedley wisely does not attempt to fix dates, but points 

 out that the fact of these two marine faunas not yet having had 

 time to intermingle, places the submergence of the Isthmus neces- 

 sarily at a very late and, probably, post-Tertiary period. 



•Report Aust. Assoc. Adv. Sc, Sydney, 1898, p. 740. 

 t These Proceedings, 1903, p.876. 



