254 
IOWA ACADEMY OP SCIENCE 
Bras 
Periods 
SUB-P. 
Series 
Terranes 
Thick 
Rocks 
ARCH 
BO- 
ZOIC 
AT.aOMTP 
Late 
Francoisian 
Skrainka 
Iron Mount’n 
Knob Lick— 
300 
500 
Diabases 
Porphyries 
Granites 
AZO- 
IC 
Not exposed- 
