The local rocks are made up of massive formations of steeply inclined sandstones and mudstones of the Silurian period dating from around 420 million years ago. These are deep water sediments, known as turbidites, formed by underwater avalanches from the continental shelf into deep ocean basins.

Click on this line for a detailed geological description.

The rocks are prone to weathering in regular patterns of lines of oval depressions or holes along the bedding planes.

Here’s another example where the rippled bedding surface has been weathered into lines of oval depressions.