Plate XV. 



Areal Map of North American Middle Devonian. 



Professor Schuchert's reconstruction of Middle Devonian 

 palseogeography at the close of Hamilton time. Partial sub- 

 mergence is indicated for the interior continental area, the two 

 principal land-masses (designated as " Lauren tia" and "Colum- 

 bia") being separated by the encroachment of the "Dakotan 

 sea." The "Ohioan sea" is represented as being in less open 

 communication with oceanic bodies on the east and south than 

 during the period immediately preceding. 



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