362 DONALD C. BARTON 
Salem limestone. The stratigraphic position of the chert beds is 
shown in the accompanying generalized section of the St. Louis 
area (Fig. 1). The Burlington-Keokuk limestone wherever exposed 
Pennsylvanian shales 
Clastic Mississippian chert 
St. Louis limestone 
Massive and argillaceous limestone 
Bed of cherty limestone 
Massive limestone, much lithographic and some argillaceous 
limestone 
Massive granular limestone with a few thin, shaly layers, 
chert common at many horizons 
Salem limestone 
Thick-bedded granular limestone 
Chert free 
Warsaw shale 
Shales, cherty limestone at the base 
Burlington-Keokuk limestone 
Shales intermixed with limestone and chert 
Thin-bedded limestone and chert 
Fern Glen limestone 
Fic. 1.—Generalized section of the St. Louis region 
in this area is consistently very cherty. The amount of chert in the 
St. Louis limestone varies considerably from place to place. The 
presence of more or less chert at the base is characteristic, but it 
