I know this doesn't look like much, but in Illinois fossils are commonly found in the center of concretions. This cave is limestone instead of the shale of the famous Mazon Creek formations, but perhaps the same principles apply?

Illinois rockhounding website has listed in the region:

"abundant echinoderm fragments-crinoids,Pentremites,Diploblastus and brachiopods-Composita,Cleiothyridina"
&
"Fossils replaced by fluorite.-- Blastoids,Brachiopods,Bryozoa"