Traces of an old east-west drainage system, buried by
glacial deposits not shown on the map, are conspicuous across
northern Ohio and Indiana. Presence of the pre-Pleistocene Teays
River is revealed as a sinuous, branching pattern of Ordovician
rocks (pink) surrounded by overlying Silurian strata (violet).
The old river channel was abandoned when its course was diverted
southward to the Ohio River drainage by the movements of early
Pleistocene ice and the emplacement of glacial deposits, probably
about 2 million years ago.