 The formation is wedge-shaped, thick (up to below Lake Erie), and laterally extensive, outcropping from Western New York to Cabot Head.It thins from southeast to northwest at around 0.6 metres per kilometre and has a dip of 3° to the south-southwest.The formation is the topmost Ordovician layer in Southern Ontario and is unconformably overlain by the Lower Silurian rocks of the Cataract Group.