BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 14, pp. 177-190, PL. 16 April 30, 1903 



SHIFTING OF FAUNAS AS A PROBLEM OF STRATIGRAPHIC 



GEOLOGY* 



BY HENRY SHALER WILLIAMS 



(Read before the Society December 30, 1902) 

 CONTENTS 



Page 



Importance of fossils to the geologist 177 



Fossil faunas and their movements 178 



Explanations of the comparative chart of sections 179 



Change in thickness of formations and its meaning 180 



The three types of sediments and their associated faunas 181 



A. The red shales and sandstones 1 81 



B. The argillaceous shales and fine grained sandstones 1 81 



C. The fine mud shales 182 



The shifting of faunas. . . 182 



Preservation of the integrity of a fauna 183 



Evidences on which this investigation rests 183 



Relation of extent of range of species to metropolis of fauna 183 



Effect of shifting on species 184 



Homceotopic and heterotopic faunas 185 



Practical rules for use of fossils in stratigraphy 186 



1. Abrupt transitions 186 



2. Slight mutations of a continuous fauna 186 



3. Lapping of two consecutive homceotopic faunas 187 



4. Detection of stages of mutation in a fauna 187 



5. Mutation associated with rapid shifting of a fauna 187 



6. Dominant and characteristic species 188 



7. Stratigraphic succession not certain evidence of chronologic succes- 



sion of faunas 188 



8. Chronologic value of first appearance of a new fauna 188 



9. Chronologic value of relative abundance of species in a fauna 189 



10. Formational equivalence not identical with faunal equivalence 189 



Importance of Fossils to the Geologist 



The geologist dealing with stratified rocks has two quite distinct tasks 

 before him. He is called upon to distinguish, define, and name the 



*Published by permission of the Director of the U. S. Geological Survey. 

 XXV— Bull. Geol. See. Am., Vol. 14, 1902 (177) 



