i8o BAILEY WILLIS 



Communication of Pacific waters through the Arctic with the seas 

 of eastern Europe and Asia is indicated by similar boreal species in 

 both regions, but the connection is not known. It may have been by 

 Behring Sea, as Stanton thinks probable, or by the Mackenzie, as 

 Willis infers. 



Marine waters (the Sundance sea) extended temporarily to Dakota, 

 Wyoming, and southern Utah. 



On the east the continent was low. The lower part of the Potomac 

 formation, long considered to be late Jurassic, is according to the 

 latest work under W. B. Clark probably "Lower" Cretaceous 

 (Comanche). The limit of the coastal plain is therefore unknown. 

 It was beyond the present coast. 



