J HE ORDOVICIAN PERIOD. 



305 



K3 



Fig. 129. — Map showing the general condition of the North American continent in 

 Mid-Ordovician (Trenton) time. The black portions represent areas where the 

 Middle Ordovician beds appear at the surface. These areas so nearly correspond 

 with the areas where the Ordovician system as a whole appears at the surface 

 that no serious error is involved if the black areas be interpreted as Ordovician 

 The various conventions of the map are the same as in Fig. 38, p. 147. 



