182 HORN EXPEDITION — SUMMARY. 



Jf we go l^ack to the close of the Cretaceous period we Hiicl tli;it after the 

 ele\atioii of the heil of the old Ui)per Cretaceous sea, tlie west and east were prohably 

 united and the conditions of climate were sucli that animal a,nd i)lant life could 

 spread across. 



Following upon this was a period during whicli a hairier existed in the form 

 partly of a marine, Ijut most largely probably in the form of a great lacustrine 

 area ; witli a diminution of this area the central part of the continent prohably 

 presented a land surface, watered by large rivers, which were fed by an aliundant 

 supply of water partly from tlie ranges in the centre, partly from tiiose fringing tlie 

 east and south-east coast. The latter were doubtless higher than at present and 

 during tlie continuance of tlicse pluvial conditions may even liave been capped with 

 snow.* At all events they ser\ed as a barrier separating a coastal fauna from an 

 internal fauna. At tlie present time the l^arrier is a climatic one, depcmdent u)ioii 

 the diflerence of rainfall, but at that time as there was an abundant rainfall and 

 conseciuently an abundant su})]ily of vegetation on Ijotli sides of the coastal ranges, 

 the barrier must have been of a diilerent nature from that which exists at the 

 present day and is probably to be found in the then greater lieight of the ranges. 



If now we suppose the marsupial fauna to have entered Australia from the 

 south aiu'oss what is now Tasmania, there was a period during which the incoming 

 fauna could travel along two routes, one leading up the eastern coast, the other 

 westwards towards what is now South Australia, across the lower country where 

 the present Dividing range sinks away at its western end. 



This primitive marsupial fauna consisted of the representatives of poly- 

 protodont forms, wliich gradually s|)read over the continent in all directions. 



On the eastern side of tlie continent over what is now the dry interior of New 

 South Wales, South Australia, and Queensland spread a vast tract of country then 

 covered with an abundant vegetation and from which there was in Northern New 

 South Wales and Southern (.Queensland, to a certain extent, a passage to the eastern 

 coastal district where the ranges were more irregular and less marked than in the 

 south-east. 



It is possible that even the early ancestors of tlie Diprotodonts reached 

 Australia from South America Imt. as yet the evidence in favour of this is very 

 scanty. 



* In liis " Geo^'rapliical History of Maninials," Mr. Lydckker status that Victoria possesses " a niouiitaiii raiiye 

 whose suiniiiits are perjietually clothed witli snow." Tliis is rather niisleadinfj, for though it is just possible tliat 

 snow may reniaiii tlirough the lenj^th of the summer in small patches in very sheltered spots on Mount Kosciusko 

 tliere is no such thin.^ as a i)erpetually snow-capped mountain, much less ran!,'e, in Australia. 



