354 T. W. STANTON CRETACEOUS-TERTIARY BOUNDARY 



intervals in an area of continental deposition are not dependent on the 

 same conditions that cause thie major breaks in marine sediments. Even 

 if it be true that there was a world-wide movement at the close of the 

 Cretaceous which caused a break between marine Cretaceous and marine 

 Eocene in all the areas where such sediments are now accessible, such a 

 movement would not necessarily affect the accumulation of continental 

 deposits of detrital material in an area already abo^'e sealevel, and in this 

 case apparently it did not affect it, On the other hand, terrestrial de- 

 posits are characteristically and necessarily irregular, and the importance 

 of breaks and unconformities in them must, therefore, be tested with 

 great care, using all kinds of .available evidence. 



The Lance formation is believed to be Cretaceous on account of its inti- 

 mate stratigraphic relation with the underlying marine Cretaceous, on 

 account of the close relationship of its vertebrate and non-marine inverte- 

 brate faunas with Cretaceous faunas, and on account of the occurrence in 

 one area of a marine Cretaceous fauna within the formation. This ma- 

 rine Cretaceous invertebrate fauna is held to establish the Cretaceous age 

 of the plants which occur in the beds beneath it, in spite of the fact that 

 these plants are said to belong to Eocene species. In other areas where 

 the Lance formation does not include a marine member, but has a thicker 

 development of strata, with a large vertebrate fauna of Mezozoic types, 

 it is a fair inference that the whole formation, with its contained flora, is 

 also of Cretaceous age. If, then, the Lance flora is in fact a Cretaceous 

 flora, notwithstanding its close relationship with Eocene floras, it is 

 obvious that the correlation of other formations with known Eocene for- 

 mations on the evidence of fossil plants alone is open to serious question. 

 In the case of the Denver and Arapa.hoe formations such a correlation is 

 directly opposed by the evidence of the vertebrate fauna, which allies 

 them closely ^vith the Lance formation. 



