208 SPENCER MOORE [SEPTEMBER 
Northern Australia was stocked. Why, then, if Australian forms are 
less highly differentiated and less capable of adaptation than Indo- 
Malayan, do we find them holding their own to-day side by side with 
the more favoured northern migrants? Assuredly this is precisely 
what we ought not to expect if the theory of northern predominance 
be sound. We ought rather to expect that those migrants from the 
south which happened to penetrate into the newly raised area would 
have been rapidly overcome by their better adapted competitors; and 
the fact that they have not been so overcome should suffice to convince 
us that, supposing Mr. Wallace’s view of the stocking of Northern 
Australia to be correct, Australian species can compete not unsuccess- 
fully with Indo-Malayan ones in the struggle for existence on a fresh 
area. In short, what Mr. Wallace supposes to have actually happened 
in Northern Australia is exactly what I have just now surmised might 
have happened in India, but for the wide stretch of imtervening sea 
which has prevented Australian forms from entering the Indian 
peninsula. 
And when we come to consider the extinctions that have taken 
place in the Australian flora since earlier tertiary times, we find 
ourselves face to face with a number of facts which contradict in toto 
the doctrine of northern predominance. The only way of escaping 
from these facts is to deny the soundness of the conclusions upon 
which they are based, that is, to throw doubt upon the determinations 
of the palaeontologisis. This is the position taken up by Professor 
Drude,’ who not only denies that a flora in many respects more 
northern than the present flora formerly flourished in Australia, but 
also questions the former presence in the European flora of many 
species belonging to orders now characteristic of Australia. Professor 
Drude cites as an example the genus Quercus, which has a wide dis- 
tribution in space, and contains species showing much adaptability to 
diverse conditions, facts rendering it difficult to understand how such a 
genus could disappear from any large area it formerly occupied. This 
instance, however, is not a very happy one, for Quercus is now known 
to flourish in New Guinea, and it may still be found living in Australia 
when the northern part of the island-continent has been more 
thoroughly examined. Moreover, we are only imperfectly informed as 
to why species become extinct. Why, for example, should so few 
Brachiopods now tenant our seas? Why is it that the great group of 
the Ammonitidae, so abundant in Mesozoic times, is represented to-day by 
but one solitary survivor, or, as some may say, by none? What reason 
can be given for the extinction of the numerous mammals characteristic 
of earlier tertiary times? The general principle underlying extinction 
is, of course, a mere commonplace to-day: it is the application of it to 
individual instances that is obscure; so much so indeed that, in spite 
of Mr. Darwin’s injunction to a contrary view, I do hold, with all due 
1 “ Handbuch der Pflanzengeographie,” s. 450. 
