DAVIS. — ROCKY MOUNTAIN TERTIARIES. 373 



mind, for its place is taken by an opinion already established in favor of 

 lacustrine origin. In all efforts to visualize the Tertiary geography of 

 the Rocky mountain region, our students are now led to imagine broad 

 sheets of level water surface, scores or hundreds of miles across, and 

 well deserving the name of " seas " often given to them in various re- 

 ports ; and the long slopes of subaerial plains to which an important 

 place may come to be given now receive very scanty consideration. 



