696 JAMES P ERR IN SMITH 



its own lines, and in all the geologic ages to come will never reach 

 the development of life as we know it elsewhere in the Era of Man. 



But is the marine fauna on the Australian shores markedly 

 different from that in other parts of the Indian Ocean, and has 

 that of the Indian Ocean no near relationships with the outside 

 world ? There are faunal provinces in these, with local charac- 

 teristics, but with gradual transition from one province to 

 another, and from one region to another through adjacent prov- 

 inces. Thus the Australian waters show a gradual transition in 

 fauna to the China Sea, and that to the Japanese marginal fauna, 

 which, in turn, show many species in common with the west 

 American region. 



If, then, the modern Pacific and Indian Ocean marginal 

 faunas were fossilized it would be no great task to correlate 

 them, although the western coast of America might not show a 

 single species in common with Australia. The laws that govern 

 the distribution and intergradationof marine faunas are the same 

 now as they have always been. All stratigraphic classification 

 and all paleontologic correlation are based ultimately on fossil 

 marine faunas. 



The reality of correlatioji. — The geologic succession of faunas 

 has some irregularities and anomalies, as shown above, but the 

 displacements of the time scale are too slight and the uniformity 

 in various separated regions too great to lay much stress on 

 homotaxis as opposed to synchronism. While homotaxial 

 strata are not necessarily synchronous in years nor in centuries, 

 the cases cited above show that they often are actually contem- 

 poraneous. But even if they were not, years and centuries count 

 little as compared with the time back to the Quaternary, and 

 still less with the great stretches of time in the Paleozoic. And 

 if a Silurian fauna still persists beyond its time by reason of local 

 favoring conditions, it is merely a transient exception, for inter- 

 regional migration soon readjusts the faunal scale in harmony 

 with the time scale. The survivals of species or faunas are the 

 exception rather than the rule, and such anachronisms can be 

 detected in the past as well as now. 



