V A GLIMPSE INTO THE PAST 143 



favour of a continental area having once existed 

 here. 



Turning to the geographical problems which 

 specially concern Tasmania, we are led to inquire 

 how recently the island was in direct land connexion 

 with the mainland of Australia. Bass's Straits 

 are two hundred miles broad, and a line can be 

 drawn through Flinders Island connecting Wilson's 

 Promontory in Victoria with Cape Portland in Tas- 

 mania, on which the depth is nowhere greater than 

 thirty-two fathoms, so that a very small elevation 

 would raise an isthmus of dry land connecting 

 Tasmania with southern Victoria. Mr. Hedley 

 brings together some important evidence derived 

 from a study of the marine shell-fish of the southern 

 Australian coast, which tends to show that this 

 Bassian Isthmus existed in comparatively recent 

 times. He shows that the shores east and west 

 of the reconstructed Bassian Isthmus are charac- 

 terized by quite distinct species and even genera 

 of Molluscs, and that very little admixture has 

 taken place between them since the isthmus has 

 been broken down. To account more satisfactorily 

 for this marked distinction he supposes that at the 

 same time as the isthmus existed, Tasmania was 

 produced southwards as dry land along what is 

 now a rather shallow submarine bank, so that the 

 marine inhabitants of the east and west coasts 

 would have had to travel further south in order to 

 intermingle, and in doing so would have been 

 subjected to greater changes of temperature than 



