Limestone scenery, Yorkshire

Image to left: shelly limestone

Fossils of coral and other creatures like crinoids (image to right) show that, around 330 million years ago, much of Britain was covered by shallow tropical seas. These shelly deposits now form the grey Carboniferous limestones of the Pennines, Peak District, south Wales and the Mendips.

These limestones contain many cracks or joints which water penetrates and begins to dissolve away the rock - eventually forming caves and underground streams and leaving the surface rather dry and barren – a type of scenery called 'Karst'.