Written in the Hills
Geology of the Ozarks, part 5
Bruce Stinchcomb

A large Ordovician cephalopod which occurs in a limestone bed on I-55 south of St. Louis
followed by showing in layers above the cephalopod (and hence slightly younger), a layer
of volcanic ash or bentonite. This is followed by a short discussion by Richard Cameron
on a bed of stromatolites which occur in strata of Lower Ordovician age which underlies
the Middle Ordovician strata carrying the cephalopod and volcanic ash beds.

Ozarks Paleontology