CONCLUSIONS 687 



If this is true, it would likewise prevent the migration of the vertebrates 

 which may have originated in the eastern province. 



But to have prevented previous migrations it must be assumed that the 

 regions were permanently separated by a water barrier from the late 

 Pottsville to the upper part of the Wabaunsee stage, or about middle 

 Monongahela time. This assumption is too sweeping to have much weight 

 until further data are at hand on which to base it. A consideration which 

 makes this proposition still more doubtful is the fact that species of plants 

 of this interval are common to both regions. 28 



Second. The alternate suggestion is that they existed contemporane- 

 ously in both regions, but as yet are known only from the eastern one, 

 where detailed study of the formations has gone on for many years. 

 There are three reasons why this supposition may be correct : 



A. These forms would only be preserved under very special conditions 

 and in isolated localities, and as a result relatively few of these forms 

 were preserved, allowing only rare chance of being exposed at the present 

 time, as is demonstrated by the extremely few vertebrate-bearing locali- 

 ties now known east of the Mississippi Eiver, where the rocks have been 

 more intensely studied. Therefore they may be present and not exposed 

 in the western interior region. 



B. They may well be present in formations in the west which are now 

 exposed and have not been discovered. So far as known, no search for 

 them has been made in the oldest red beds of Pottawatomie and Seminole 

 counties. In this connection it should be mentioned that exposures in 

 the red beds of the Wichita and Clear Fork stages are vastly more favor- 

 able for finding fossils than are more thoroughly vegetation-covered re- 

 gions farther east, in the lower formations of Texas and Oklahoma. 



C. The remains of an amphibian and a reptile were found in the 

 Wabaunsee formation of Kansas, probably at about the level of the middle 

 Monongahela stage of Pennsylvania and West Virginia. It is the writer's 

 opinion that when the outcrops of the rocks have all been thoroughly 

 searched for fossil air-breathing vertebrates, they will be found in western 

 beds which are nearly as old as those from which they are known east of 

 the Mississippi River. 



Conclusions 



1. It seems that the correlation of the eastern and western interior 

 regions based on evidence of fossil animals and plants is well established. 

 It is about as harmonious as might be expected from these two types of 

 evidence. 



88 D. White: U. S. fleol. Survey Bull. 211, 1903, pp. 110-115. 



