The Guelph Formation is at the top of the Lockport Group. It has been called the "Vernon Transition Zone" due to thin beds and laminations between carbonates, claystones and evaporates. Its base is delimited by a stromatolite bed.
Below the Guelph is the Eramosa Formation. This formation is typically a thinly laminated packstone and grainstone. There are stromatolite beds as well as corals preserved in this formation. Near the base the unit becomes vuggy. Again the top of this formation is marked by a sharp change between grainstone and a stromatolite bed.