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-Malayau 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 intervening 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 palaeontologists. This is the position taken up by Professor 

 Drude, 1 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. 



