BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 21, pp. 285-294 JUNE 25, 1910 



MIGEATION AND SHIFTIIS^G OF DEVOXIAlSr FAUXAS^ 



BY HENRY S. WILLIA2IS 



{Presented in ahsiract before tlie Paleonto/ogical Society Dec. 31, 1909) 



CONTENTS 



Page 



The hypotheses of recurrence and shifting of faunas stated 285 



Facts on which the hypotheses rest 286 



Catskill sedimentation 286 



Reversal of order in succession of faunas 286 



Recurrent Hamilton fauna 287 



Alternate appearance of diverse fossiliferous zones 287 



Limited range of recurrent species 288 



Interpretation of the facts : 289 



Shifting of faunas 289 



Lithologic changes not sufficient to account for differences in faunas. . 289 



Difference in ocean waters presumed 289 



Migration of species and shifting of faunas contrasted 290 



Changed environment cause of both migration and shifting 291 



Close adjustment of species of a shifting fauna 291 



Evidence of migration 291 



Recurrence 292 



Theoretical problems involved 292 



Evidence of f aunal continuity 292 



Rare and dominant species 292 



Magna faunas and local special faunas 293 



Fixed and fluctuating characters 293 



Difficulties in establishing evidence of strict contemporaneity 294 



The Hypotheses of Eecurrexce axd shifttxg Faunas stated 



In 1881 I presented before the American Association for the Advance- 

 ment of Science the first definite announcement of the hypothesis of re- 

 current faunas, applying it to the fauna of the Marcellus, Genesee, and 

 Ithaca black shales of new York, which I then conceived to be represented 



1 Manuscript received by the Secretary of the Geological Society April 23. 1910. 

 XX— Bull. Geol. Soc. Am.. Vol. 21. 1009 (285) 



