310 PROCEEDINGS OF SECTION C. 



therefore the work before the Australian geologist, however 

 slow in progress, will be more satisfactorily advanced if 

 we stick close to the evidences afforded by the unmistakable 

 observed order of succession of local stratigraphy in the first 

 place ; and afterwards, by carefvdly observing the nature of the 

 contained fossils in each succeeding horizon, gradually build up 

 the locally true order of biological succession. The dejDendence 

 upon the succession of rocks of distant regions, as based upon the 

 affinities of organic remains, though temptingly convenient, must 

 assuredly prove to be a Will-o'-the-Wisp chase leading to geological 

 disaster. 



The order of biological progression depends largely upon local 

 external conditions, and unless we assume what is impossible, 

 that environment varies in every separate region at the same time 

 and in the same degree, the rate of biological variation or develop- 

 ment must almost of necessity vary with the locality. 



This helps to explain the greater differences exhibited by the 

 contemporary floras of two widely separated regions, than is shown 

 by the contemporary faunas of the same regions. 



As already suggested by me,* the closer parallelism between 

 the marine remains of two widely separated regions is probably due 

 to the greater facilities for more rapid dittusion of types among the 

 marine inhabitants of a continuous sea, as compared with the 

 slov.'er diffusion of terrestrial organisms, barred as it must often 

 have been by wide tracts of sea, and other physical obstructions. 

 This conclusion is borne out by the illustrious Darwin,* who states, 

 " The process of diffusion would often be very slow, depending on 

 climatal and geographical changes, on strange accidents, and on 

 the gradual acclimitisation of new species to the various climates 

 through which they might have to pass, but in the course of time 

 the dominant forms would generally succeed in spreading and 

 would ultimately prevail. The diffusion would, it is probable, be 

 slower with the terrestrial inhabitants of distinct continents, 

 tha^n with the marine inhabitants of the continuous sea. We 

 might thei'efore expect to find, as we do find, a less strict degree 

 of parallelism in the succession of the productions of the land, 

 than with those of the sea." 



In summing up the various considerations touched upon in this 

 paper, I anticipate your verdict will be, that Australian geologists 

 cannot safely rely upon the order of succession of the characteristic 

 genera of fossil plants of a far distant region in the determination 

 of the order and relationship of Australian terrestrial formations ; 

 and that even within its own wide borders, covering an area 

 nearly equal to that of the whole of Europe, considerable differences 

 may be expected in the biology and minor subdivision of systems, 

 as developed in some of its widely separated colonies. 



* Papers and Proc. R. Soc. Tas. 1886, p. 166. 

 t Origin of Species, pp. 229-230. 



