GEOLOGICAL RELATIONS. 5 



of the North American continent were distinctly outlined, including the 

 Atlantic and Rocky IVIountain areas. The work of later geological pe- 

 riods seems to have been the filling up the bays and sounds between the 



or 



irO RTH AMER ICA. 

 I ms Xozorc 



<■. ^ Afesozoic. 



y|-p«^^]^-^>^\ ^ Cenozoic 



great islands, elevating the consolidated mass into a continental area, 

 and probably submerging other equally important islands beneath the 

 Atlantic and Pacific oceans. 



Seroml Although the Rocky IMountain Eozoic area existed very early, 

 it seems to have oscillated considerably during the Paleozoic and Meso- 

 zoic periods, sometimes elevated and often submerged, while the Eozoic 

 districts of the east remained elevated above the sea from the verj- first. 

 This is shown parti)' b}- the gradual extension westwards of the sub- 

 marine deposits. East of the I\Iississippi river there is scarcely anything 

 in the interior basin later than the coal measures. Then comes the 



