CHAPTER XXIV.
THE COAL OR CARBONIFEROUS GROUP.
Carboniferous strata in the south-west of England--Superposition of Coal-measures to Mountain limestone--Departure from this type in north of England and Scotland--Section in South Wales--Underclays with Stigmaria--Carboniferous Flora--Ferns, Lepidodendra, Calamites, Asterophyllites, Sigillariae, Stigmariae,--Coniferae--Endogens--Absence of Exogens--Coal, how formed--Erect fossil trees--Parkfield Colliery--St. Etienne, Coal-field--Oblique trees or snags--Fossil forests in Nova Scotia--Brackish water and marine strata--Origin of Clay-iron-stone 308