368 



E. O. ULRICH REVISION OP THE PALEOZOIC SYSTEMS 



channel on the west side of Ozarkia, being known in central Oklahoma. 

 Though entirely unknown in the western half of North America, in the 



KIMMSWICK OR NORMANSKIUL GRAPTOLITE 



ECHIN05PHAE.RITES FAUN* CHANNELS 



P'AC/f/C /A/MS/ON 



Figure 7. — Map of North America, showing interlapping late Black River and early 

 Trenton Invasions from the Arctic, Atlantic, Oulf of Mexico, and Pacific Sides 



eastern half, besides the areas mentioned, the Decorah fauna is recog- 

 nized at many localities north of New York. With even a small collec- 



