THE VICTORIAN NATURALIST. 141 



But how did the South American affinities come about ? We 

 have two theories. 



I. — Wallace considers a two-fold current of life flowed into 

 Australia from the Old World — one current by way of Himalayas, 

 Southern Asia, Borneo, Moluccas, and New Guinea, thence to 

 Australia ; the other current by way of the American continent, 

 whose mountain chain has formed the most effective agent in 

 aiding the southward migration of arctic and north temperate 

 flora, and these travellers found a home in antarctic continents 

 and islands. New Zealand, Tasmania, and Australia itself. The 

 route is easily marked out. South of Cape Horn, 500 miles 

 distant, are the Shetland Islands and Graham's Land, whence 

 antarctic continent probably extends round South Pole to Victoria 

 Land, and thence to Adele Land. Young Island, 12,000 feet 

 high, is about 750 miles south of Macquarie Islands, which are 

 outliers of New Zealand. Other islands may have existed, and 

 barrier of the remaining seas may have been overcome by the 

 ■currents in the water (which often carry plants and small animals 

 to great distances), by the wind, and by petrels (which carry 

 seeds, &c.) We must also remember the probable greater ex- 

 tension of southern lands during the warm Miocene period. When 

 cold returned, and land again became iceclad, the plants would 

 be crowded towards the margin of the antarctic land, and many 

 would find their way across the sea on floating icebergs. Some 

 forms of life are carried to great distances by floating ice-fields. 

 The marsupials were not, he thinks, emigrants from America to 

 Australia, but both were derived from Europe — American from a 

 ■northern connection, and Australian through an Asiatic. 



In an article on "The Discovery of an Australian-like Marsupial 

 in South America," R. Lydekker writes in Nature, 5th May, 1892 : 

 — " Mr. Wallace's explanation that marsupials came from Europe 

 in both cases will not, on his own showing, hold good for close 

 resemblance between this American and the Tasmanian forms, 

 since it is quite impossible to believe that two such similar forms 

 could have maintained their likeness in such remote regions as 

 Patagonia and Tasmania after having diverged from a common 

 European ancestor as far back as Jurassic period." 



II. — The second theory to account for affinity with South 

 America is Prof. Hutton's, of New Zealand. He analyzes 

 affinities of fauna in this way : — (i) Mammalia, character Aus- 

 tralian ; (2) birds, more nearly African than American ; (3) frogs, 

 more nearly South American than elsewhere : therefore frogs did 

 not come by same route as birds, for where frogs could pass birds 

 •could. Map showing 1,000 fathoms will account for birds, but 

 frogs and freshwater fish, &c., came from South America before 

 arrival of the birds. 



A vast plateau — nowhere less than 2,000 fathoms below sea 



