432 Capt. F. W. Hutton on the Origin of the 
impossible, by assuming any reasonable amount of extermina- 
tion, to make the distribution of birds accord with that of the 
frogs. The lines of migration of frogs must therefore have 
been different from those of birds. Again, Mr. Wallace 
himself allows that salt water is almost a complete barrier to 
the dispersal of frogs * ; consequently where frogs could pass 
birds could pass also; and as the former have passed between 
Australia and South America, but not the latter, it follows 
that the two could not have spread together, but each must 
have pursued a different route at a different time. And as 
the present shape of the land accounts for the distribution of 
the birds, the distribution of the frogs must have taken place 
before the present groups of birds were in existence. But 
birds of many kinds were abundant in Europe and in 
America in Eocene times; and as we know that penguins 
inhabited New Zealand at the same period, it is probable 
that birds then existed in Australia also. Consequently 
the South-American migration must have taken place be- 
fore the Hocene, and cannot be referred to a warm Miocene 
period. Evidently, therefore, the existence of the South- 
American element ‘in the Australian fauna and flora requires 
some explanation which Mr. Wallace’s hypothesis does not 
supply. 
It was these considerations, together with the fact that the 
earthquake-wave of 1868 had proved that the average depth 
of the South Pacific Ocean was not great, which led me in 
1872 to propose the hypothesis that in the Lower Cretaceous 
period an antarctic continent extended northwards into Poly- 
nesia, connecting Australia with South America and, perhaps, 
with South Africa. I introduced the African connexion 
solely to account for the distribution of the Struthious birds ; 
but I am now satisfied that Mr. Wallace’s explanation of 
the spread of these birds from the north is more correct; and 
no reason therefore remains for supposing that Australia was 
ever connected with Africa. But the evidence of a connexion 
with South America is stronger than ever. Nevertheless I 
now abandon the idea of an extensive antarctic continent, 
because the soundings that have been lately taken in the 
Pacific Ocean have shown that such a supposition is highly 
improbable. At the same time these soundings have made it 
clear how the connexion really took place. 
The surveys of the ‘Tuscarora,’ the ‘Gazelle,’ and the 
‘Challenger’ have proved that a vast submarine plateau, 
nowhere more than 2000 fathoms below the sea-level, runs 
* ‘Geographical Distribution of Animals,’ i. p, 416, 
