Stratigraphy: Carboniferous metamorphosed sedimentary rocks with ages ranging from approximately 354 to 280 million years before present.

Distribution: The rocks of Yuen Long Formation do not occur at outcrop, but have been penetrated in boreholes, principally in the Yuen Long and Ma On Shan areas.

Lithology: The Yuen Long Formation consists of white to dark grey or black calcite and dolomite marble.

Depositional Environment: The Yuen Long Formation is interpreted as having been originally deposited as a pure to slightly impure limestone in a shallow water platform setting.

(Grey to dark grey, fine-grained dolomitic marble of the Long Ping Member, Yuen Long Formation)