STRATIGRAPHIC SUMMARY. 619 



Upper Ordovicic. 



Cincinnatian 68-250 ft. 



{hiatus) 



Galena limestone "I 



Middle Ordovicic. I 300-440 ft. 



Stones River limestone J 



Upper St. Peter sandstone 1 



Lower Ordovicic. 1 150-275 ft. 



Lower St. Peter sandstone J 



Lower Magnesian (Lower Beek- 



mantown) 45o-8i i ft. 



SUBFORMATION. 



Upper (?) Cambric sandstones. 



In Iowa the following subdivisions of the Ordovicic have re- 

 cently been published. ^^ The classification here adopted being 

 added : 



SUPERFORMATION. 



Siluric. 

 Upper Ordovicic. 



10. Brainard shale. 

 9. Fort Atkinson limestone. 

 8. Clermont shale. 

 7. Elgin shaly limestone. 



{probably a hiatus) 

 6. Galena limestone. 



Middle Ordovicic. 



5. Decorah (green) shale. 

 4. Platteville limestone. 

 3. Glenwood shale. 

 2. Saint Peter sandstone. 



Lower Ordovicic. 



I. Oneota dolomite. 

 (Base not exposed.) 

 According to Sardeson the Decorah shale is the equivalent of 



"la. Geol. Survey Annual Report, Vol. i6, p. 60. 



