The unit outcrops in New York, Ontario, Michigan, Wisconsin, and Illinois.

The entire unit is composed of dolomite, with the exception of the Gasport which can be limestone, as well as occasional chert nodules.

It has been called the "Vernon Transition Zone" due to thin beds and laminations between carbonates, claystones and evaporates.

This formation is typically a thinly laminated packstone and grainstone.

Again the top of this formation is marked by a sharp change between grainstone and a stromatolite bed.