188 J. Hall on Carboniferous Limestones of Mississippi Valley. 
D. D. Owen are, first, an upper and lower series, each of which 
is again subdivided into several distinct beds or groups. For 
the sake of comparison, this table of Dr. Owen’s is here given. 
“SECTION OF SUB-CARBONIFEROUS LIMESTONES OF IOWA. 
Coal Measures. 
20 feet. | Upper concretionary limestone. 
10 feet. | Gritstones. 
30 feet. | Lower concretionary limestones. 
10 feet. | Gritstones. 
10 feet. | Magnesian limestone. 
30 feet. | Geodiferous beds. 
50 feet. | Archimedes limestone. 
15 feet. | Shell beds. 
15 feet. | Keokuk cherty limestone. 
70 feet. | Reddish brown encrinital group of Hannibal. 
55 feet. | Encrinital group of Burlington. 
75 feet. | Argillo-calcareous group, Evans’ Falls.” 
