Dolomitic Carboniferous Limestone
These limestones contain the fossils of extinct animals. These creatures lived in warm, shallow seas, that included sufficient lime for building their shells.
When these rocks were forming there was a chain of great mountains stretching across mid Wales, and to the north and south were marine basins. These rocks fromed in the southern sea and there are ripple marks, like those seen on modern beaches, which you can see on the surfaces of some of these blocks.
Quarried for steel
Because it contains a lot of magnesium, this sort of limestone is known as Dolomite. Crushed and added to iron ore, Dolomite makes purer steel, and so it was much quarried in Wales for use in the steel industry.
You may notice that there are not many varieties of lichens on this rock. It lacks nutrients and most lichens cannot tolerate high levels of lime. But some lichens live beneath the surface and are only visible when they produce fruiting bodies.
Where do these rocks come from?
Cornelly Quarry, Pyle, Mid Glamorgan