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act as checks to distribution within the period covered by 

 any one sub-division of a system ? 



It is difficult to answer such questions satisfactorily, but if 

 we take each point carefully into consideration we must 

 arrive roughly at such conclusions as the following : — 



1. It is improbable that all species had their origin in one 

 particular hemisphere. 



2. It is probable that some species originated in the 

 Northern Hemisphere, while others had their origin in the 

 Southern. 



3. It is reasonable to assume when species or genera have 

 spread from the centre of origin to another hemisphere 

 that a considerable period of time must have elapsed. 



4. Where such world-wide distribution of forms has 

 taken place we can imagine in either hemisphere their 

 appearance in one local formation or series, some of them 

 having originated locally within the age of the system or 

 formation, while others were immigrants from an opposite 

 hemisphere, which might date their original appearance to 

 an anterior period in some spot on the opposite hemisphere, 

 where it is natural to expect a wide difference in the form 

 and character of their associates as compared with those to 

 be met with in the subsequent position to which they 

 migrated. 



If this very reasonable supposition bo admitted, and I do 

 not see why it should be rejected, of what value is the classi- 

 fication of Australian rocks which too slavishly follows the 

 sub-divisions of great periods or systems as they occur in 

 Europe, upon the mere evidence of two or three genera 

 whose association in the rocks of a particular horizon in 

 Europe may only be of local significance ? No better illus- 

 tration of the utter futility of such modes of classification 

 can be given than that indicated by the peculiar association 

 of animals and plants in Australia, within the Upper 

 Palaeozoic age, as compared with the associated animals and 

 plants in the European rocks of the same period. For 

 whatever disputes there may have been regarding the 

 relationship of the Upper Palaeozoic marine beds of Australia 

 with the lower coal measures, chiefly containing plants 

 belonging to the genera Glossopteris, Gangamopteris, and 

 Noeggeraihiopsis, there is now not the slightest doubt but 

 that these plants are as characteristic and are as intimately 

 related with the carboniferous marine beds of Australasia as 

 the characteristic genera Pecopteris, Neuropteris, Alethopteris, 

 Sphenopteris, Lepidodendron, Sigillaria, and Calamites are 

 with respect to the carboniferous marine beds of Europe. 



Judging from the marine organisms alone there are little 

 difficulties in the way of proving the homotaxial relationship 



