The Middlesex Formation is a carbon rich black shale geologic formation found in the Appalachian Basin.

It represents one of several transgressive events (rising sea levels) during the Late Devonian.

The Middlesex is a laminated, dark grey to black formation comprising mudstone and siltstone.

There are also sparse sand and silt layers, suggesting that they were single event deposits.

This article about a specific stratigraphic formation in New York state is a stub.