The Geddes Limestone was defined by Wheeler and Lemmon (1939) for strata between the massive Eldorado dolomite and the Secret Canyon Shale. It is named for exposures near the Geddes Mine in Secret Canyon near Eureka.

The Geddes Limestone is middle Middle Cambrian in age.

The Geddes is a dark-blue gray to black, well-bedded, fine-grained, carbonaceous limestone with shale partings and small amounts of black nodular chert (Nolan and others, 1956). Beds range in thickness from 2 to 8 inches and commonly weather to a purple or reddish color (Roberts and others, 1967). The contact of the Geddes with the underlying Eldorado Dolomite is gradational and locally the two formations interfinger with one another (Roberts and others, 1967).

The Geddes Limestone is often tightly folded, and is 330 feet thick at its type section.

The Geddes Limestone is only exposed in the Eureka area.

The details of the depositional setting of the Geddes Limestone are poorly understood. In general the Geddes represents shallow marine shelf sedimentation.