376 F. H. KNOWLTON 



the Lance, Arapahoe and Denver formations may be mere "phases 

 of the Laramie." Whether the Laramie and various post-Laramie 

 beds were deposited and later removed throughout the Dakotas, 

 Montana, and Wyoming, is not at present known, but certain 

 it is that the unconformity at the base of the Lance formation 

 represents the time interval during which in other areas they were 

 laid down and subsequently removed in whole or in part. There- 

 fore, in the opinion of the writer, this unconformity is an impor- 

 tant one and must be so recognized in American geology. 



Since it has been demonstrated that the Lance formation is so 

 inseparably associated with the Fort Union — that is, without a 

 trace of an unconformity — and is separated from the underlying 

 formations by an unconformity of such extent, this point becomes 

 more clearly than ever the logical point at which to draw the line 

 between Cretaceous and Tertiary. In establishing this line the 

 stratigraphic, lithologic, and paleobotanical criteria are believed 

 to be more competent than any other evidence thus far brought 

 forward. 



