424 ILLINOIS STATE ACADEMY OF SCIENCE 



Core from Hamilton County also shows two zones of 

 Fusnlinas which are here but 20 feet apart. These have 

 not been carefully studied and the relations are not posi- 

 tively determined. The upper of the two limestones has 

 been called the No. 6 cap rock. In the southwestern part 

 of Montgomery County along Piasa Creek there have 

 been obtained samples of Fusulina distinctly different 

 from those of the No. 6 limestone. It is a long, relatively 

 slender type which appears comparable to those reported 

 from Belleville and from Peoria. 



5. Inferences as to distribution: 



1. It appears that no Fusulinas are found below the 

 McLeansboro or possibly upper Carbondale beds. 



2. There is at least one zone of Fusulina like Girtyina 

 ventricosa lying distinctly above it near what has been 

 called No. 8 coal. To this zone are referred tentatively 

 the upper Fusulinas of Peoria, Belleville, and Shelby 

 County, and those found on Piasa Creek. 



3. There is but one zone yet noted of the true Fusulina 

 represented by Fusulina secalica occurring high up in 

 the McLeansboro series in Cumberland County. The 

 true Girtyina ventricosa is to be restricted to the cap 

 rock of No. 6 coal and to have a very wide distribution 

 over the Eastern Interior Coal Basin. 



6. Implications as to correlation: 



1. There is no evidence to indicate that Girtyina ven- 

 tricosa may not be retained as an index fossil for the cap 

 limestone of No. 6 coal. 



2. On this basis the margin of the Eastern Interior 

 Basin is marked by McLeansboro beds rather than Potts- 

 ville and lower Carbondale. 



3. This indicates a very extensive overlap of Late 

 Pennsylvanian beds over the Pottsville and early Car- 

 bondale areas of deposition. This modification applies 

 equally to Illinois, the Des Moines section in Muscatine 

 and Scott counties of Iowa, and western Indiana. 



