46 



tioii, I am led to conclude that, as the insetting cold advanced 

 towards the equator, the semi-tropical fauna then inhabiting 

 the South Australian area would migrate or creep northward, 

 as their natural habitat receded in that direction; and from the 

 profundity of sea-depths which separate adjacent lands from 

 the southern shores of Australia, the South Australian shores 

 would remain depopulated of the higher orders of mollusca 

 so long as this state of cold prevailed. As the cold reached 

 its severest point the sea increased upon the land in the latitude 

 of Adelaide to the extent of from 800 feet to 1,000 feet, and 

 the deposits laid down in that azoic sea when elevated into dry- 

 land would assuredly be void of most if not all indications of 

 marine life. 



That a somewhat similar phenomenon occurred during middle 

 Tertiary times might have been noted, and that one or more of 

 the species common in the Miocene beds of South Australia mi- 

 grated northwards at the close of that period and are now found 

 inhabitants of the tropical seas. 



It would appear that a somewhat similar theory arose in 

 the mind of Mr. Selwyn to the one I have advanced. He 

 states at page 25 of his " Physical Geology and Geography of 

 the Colony of Victoria": — "The absence of any evidence of 

 marine life may probably be fully accounted for by the charac- 

 ter of the deposits, which indicate physical conditions that 

 must have been highly unfavourable to the development of 

 animal life in the area." According to this quotation it seems 

 that the same non-fossiliferous conditions extend throughout 

 the recent deposits of Victoria as prevails in South Australia. 

 Being assured then that so great a similarity prevails '^alceon- 

 iolocjicaUy throughout the recent deposits over so widespread a 

 tract of the Australian continent, suggests that these effects 

 were produced by some equally widespread a cause. 



By reference to a map of the world we observe that no 

 analogy exists in the distribution of sea and land in the 

 northern and southern hemispheres. In every case the con- 

 tinents that are situated within the former enjoy a diversity of 

 temperature such as that hemisphere sustains ; consequently the 

 inhabitants of these lands and the adjoining seas have free 

 access to accommodate themselves to that degree of tempera- 

 ture best adapted to their wants. If the cold of the frigid 

 zone for a time be extended equatorwise, the inhabitants, both 

 of land and sea, of these regions have natural facilities afforded 

 to shift their area of occupancy ; or if the heat for the time 

 being of the torrid zone incline towards the north the abode of 

 the inhabitants of these regions is similarly extended. In 

 short, throughout the northern hemisphere, at whatever 

 parallel of north latitude the permanent frost-line may be 



