BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 26, pp. 303-314 August 17, i915 



PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



EEASONS FOE EEGAEDING THE MOEEISO^T AN" IJsiTEO- 

 DUCTOEY CEETACEOUS FOEMATION ^ 



BY WILLIS T. LEE 



(Read hefore the Piil cimlolodlcdl Sociely Deremher SO, 107J/.) 



CONTENTS 



Page 



Introduction 303 



Faunal considerations 304 



Physical considerations 305 



In general 305 



Principles 306 



Equivalents and associates of the Morrison 307 



Character of the Morrison 308 



Structural relations 309 



Physiographic conditions 310 



Conclusions 313 



References 313 



Introduction 



The position in the time scale of a non-marine formation like the 

 Morrison is difficult to determine unless it can be fixed in some way in 

 a succession of conformable deposits, some of which at least are marine. 

 Geologists have w^orked along the line of marine succession since the 

 origin of their science, and on this succession mainly the commonly ac- 

 cepted stratigraphic columns and time scales are based. However, after 

 all the excellent work of paleontologists, one of their nimiber informs us 

 that fossils alone too often lead to erroneous conclusions, and that "dias- 

 trophism affords the only means of finally attaining a reasonable, accu- 

 rate, and systematically constructed classification" (1, page 005)." If this 



1 Coutrlbution to the symposium held at tlio Philadelphia meeting of the Society De- 

 cember .■'.0. 1014. 



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

 Manuscript received by the Secretary of the Society April ?,. 1015. 

 a For references see list at end of paper, p. 31.3. 



(303) 



