18 MISSISSIPPIAN BRACHIOPODA 



SECTION AT WARSAW, ILLINOIS 



St. Louis limestone. Feet 



11. Dense, bluish, brecciated limestone 10 



Salem limestone. 



10. More or less cross-bedded limestone, yellow on weathered 

 surfaces and granular in appearance, containing large 

 numbers of broken bryozoans; locally replaced by a 



calcareous grit or sandstone 8 



Warsaw formation. 



9. Thin-bedded bluish limestone, interbedded with cal- 

 careous shales. Fossil bryozoans abundant, especially 



Lioclema punctata and Archimedes wortheni 18 



8. Fine blue shale 3 



7. Hard, light-colored limestone, with few poorly preserved 



fossils 4 



6. Fine blue shale 8 



5. Magnesian limestone with shaly bands. Fossils poorly 



preserved and as a rule rare, mostly bryozoans 8 



Keokuk limestone. 



4. Bluish shales with numerous geodes which are generally 

 smaller than those in the magnesian limestone beds 



below 21 



3. Magnesian limestone with chert bands 3 



2. Magnesian limestone with numerous geodes. Some beds 

 more or less shaly. Geodes more numerous in the 

 middle part of the bed. Fossils poorly preserved and 



rather rare, mostly imperfect bryozoans 15 



1. Blue or gray crystalline limestone with many fossils. 

 Thickness not known, the bed extending below river 

 level (exposed) 15 



The dominant characteristic of the Warsaw formation is the presence 

 of bluish shale with subordinate beds of limestone, but because of the 

 softness of the beds they are rarely well exposed at the surface. The 

 geographical distribution of the formation follows that of the Keokuk 

 limestone wherever the full thickness of that formation is present north 

 of the latitude of St. Louis. The formation is well developed in the 

 Meramec basin in the St. Louis quadrangle, but southward it is seemingly 

 absent, allowing the superjacent Salem or Spergen limestone to rest 

 directly upon the Keokuk formation. For example, in Monroe County, 

 Illinois, almost the entire Keokuk formation is represented by shales, 

 with subordinate bands of limestone, which closely simulate the Warsaw, 

 but the upper limit of these beds is marked by a conspicuous limestone 

 layer from one to several feet in thickness, which is crowded with speci- 

 mens of a species of Spirifer. In the Meramec Highlands section in the 

 St. Louis quadrangle, this same Spirifer bed occurs about 50 feet below 

 the base of the Salem limestone. These intervening Warsaw beds are 

 wanting in the Monroe County section. 



