It is part of a large reef structure dating back to the Silurian period.

[2] The Gasport represents a period of reef building with the upper Pekin member containing large Stromatolite structures.

[3] The lower Gothic Hill member contains Bryozones, corals, and crinoids.

The upper Pekin member is a dark grey argillaceous limestone.

At its base there is an erosional disconformity contact with the underlaying Clinton Group.