362 



HISTORICAL GEOLOGY 



eastern United States afforded conditions for the rapid and 

 conflicting evolution of species. At the outset of the period 



FIG. 373. Supposed geography of North America in late Devonian time. 

 The dotted pattern represents sediments on land. The limits of the land 

 mass north and south of the United States are wholly unknown. 



the animals of the sea were confined to the edges of the con- 

 tinent and such bays as lapped over its surface. Being iso- 



