The Group comprises a lower
unit of coarse
sandstones,
siltstones,
mudstone, and
limestones with thin
coals and
ironstones known as the Lower Limestone Formation, an overlying sequence of similar rocks known as the Limestone Coal Formation, then an Upper Limestone Formation and at its top the sandstones of the Passage Formation. This last formation also includes
fireclays, siltstones, mudstones, ironstones, coal and
seatrocks. The Clackmannan Group conformably overlays the rocks of the
Strathclyde Group and underlays the
Coal Measures, this latter boundary also being
conformable. == Paleontology ==