28o STANTON 



assuming that all Ceratopsia everywhere must be above such an uncon- 

 formity, and especially has this ceased to be valid reasoning since it 

 has been proved that the Judith River Ceratopsia are in a formation 

 intercalated between marine formations of the conformable Upper 

 Cretaceous series. 



Physiographic Conditions Near the Close of the 

 Cretaceous. 



Before discussing the paleontologic evidence of the age of the 

 " Ceratops beds" it is desirable to consider briefly the relations of land 

 and sea and the general conditions of sedimentation in the great Interior 

 Region in late Cretaceous and early Tertiary time. It is well known 

 that during the Benton epoch the sea covered practically all parts of that 

 region in which Cretaceous rocks are now found. Only locally along the 

 western margin were there estuaries and marshes in which coal was 

 formed and from which purely marine life was excluded. Soon after 

 the Benton, however, large areas west of the Front Range in Colorado 

 and Wyoming and west of the loSth meridian in Montana previously 

 covered by the sea began to emerge, either by uplift or by filling of the 

 basins with sediment, and as they came up to sea level or a few feet 

 above it land and marsh plants became established and all the con- 

 ditions became favorable for the formation of coal beds. Land ani- 

 mals also came in and the streams and fresh-water lagoons received 

 their appropriate population from adjacent areas while the bays and 

 estuaries were inhabited by brackish- water forms. Topographic con- 

 ditions must have been such that sedimentation was practically con- 

 tinuous from the marine deposits to the land and fresh-water sedi- 

 ments. Such deposits are represented by the Mesaverde formation 

 on the south and by the Eagle and Judith River formations on the 

 north. The neighboring land masses must have formed large areas 

 and have had considerable elevation in order to furnish the immense 

 thickness of Upper Cretaceous sediments known in this region. 



The uplift was not uniform nor continuous. There were oscilla- 

 tions so that occasionally brackish-water or marine deposits were 

 brought above those of land and fresh-water origin, and it is probable 

 that these oscillations were not always synchronous througiiout the 

 region. Even in areas where marine waters did not come in for a long 



