To create meaningful structural maps related to geologic processes from well log data, one must consistently select the boundaries of the formations in question. Different workers use a variety of names and markers for the Lower Ordovician strata in Ohio, causing confusion and discrepancies in correlation and interpretation. So, it is apparent that some standard must be established.

The currently accepted nomenclature, in ascending order, is the Knox Dolomite (upper region), Glenwood or Wells Creek Formation, Black River Limestone, and Trenton Limestone. The Ohio Geological Survey has generated a sample log for these formations based on data from several wells in Licking County of central Ohio. One cannot use this as a type log for the entire state, particularly when choosing the top of the Black River Limestone. Previously, a very thorough chemical description and correlation was made and several bentonite beds were used to define the Black River. Still, this description is not easily distinguished on the geophysical logs. However, assuming the postulate that the Trenton and Black River were deposited contemporaneously and those names have no time significance, nly three formations need be considered and can be consistently recognized on any log in the state.

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