44 CROSS 



brought forward by Scott to account for the extinction of the Miocene 

 fauna of Patagonia. If the disappearance of the Ceratopsia and 

 associated reptilian forms may possibly have been due to the great 

 volcanic outbursts of the Shoshone epoch, it is nevertheless true that 

 no ash beds have been found in which their remains occur in per- 

 fect condition, as is the case in the other instances referred to. The 

 Denver beds are for the most part not ash beds. It is of course 

 possible that such beds were eroded before the Fort Union epoch, 

 but this explanation is certainly as yet merely a speculation. 



Where a gradual change takes place from one set of conditions to 

 another various groups of animals and plants of the earlier period 

 will adjust themselves with varying rapidity and success to the con- 

 ditions of the later time, and some may disappear through the lack 

 of the power of adjustment. The forms which survive longest are 

 manifestly not those which mark the change in conditions. The 

 vertebrate fauna can logically be used to limit the Cretaceous of the 

 Rocky Mountain province only on the basis of a time correlation 

 through those forms with some well established section elsewhere. 

 As far as I know there is no such section on the American continent. 

 Certain marked resemblances have been pointed out between the 

 Ceratops fauna and that of the Gosau formation in Austria, which, 

 after much discussion has been referred to the uppermost Creta- 

 ceous. But it is of much importance in citing this resemblance to 

 know whether it is the Triceratops fauna of the Shoshone group, the 

 forms of the Judith River Cretaceous, or possibly a more primitive 

 fauna, which is most closely related to that of the Gosau beds. 



The question as to where the Cretaceous- Eocene line shall be 

 drawn in the Rocky Mountain province is one to be decided on 

 broad grounds and in closing I wish to quote the philosophical 

 views of Dr. C. A. White, a biologist, paleontologist, and strati- 

 grapher, expressed in regard to this very question nearly 20 years 

 ago, after discussing the evidence of the Arapahoe and Denver beds. 

 Referring to precise determinations of the age of formations solely 

 on fossil evidence. Dr. White remarks: 



Those paleontologists who make this unwarranted application of their 

 science to systematic geology, all use the scheme of classification that has 

 been established for Europe, and use it as if it were of infallible a})i)lication 

 to all other parts of the world, and also as if it were already absolutely 



