Characteristics
Carboniferous Limestone is a sedimentary rock made of calcium carbonate. It is generally light-grey in colour, and is hard. It was formed in warm, shallow tropical seas teeming with life. The rock is made up of the shells and hard parts of millions of sea creatures, some up to 30 cm in length, encased in carbonate mud. Fossil corals, brachiopods and crinoids are very much in evidence as components of Carboniferous Limestone; indeed the rock is full of fossils.
Carboniferous Limestone has horizontal layers (beds) with bedding planes, and vertical joints. These joints are weaknesses in the rock, which are exploited by agents of both denudation and weathering. They also lead to the most important characteristic of Carboniferous Limestone - its permeability. Water seeps through the joints in the limestone. This creates a landscape that lacks surface drainage but which has all manner of characteristic surface and subsurface features. The Carboniferous Limestone has been folded and faulted by massive Earth movements which can be seen by the fact that the rocks are now above sea-level and no longer horizontal. The rocks generally dip (slope) gently eastwards and, in some places, clear folds in the rock can be seen especially at the Great Orme and Bryn Alyn (Denbighshire).
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