The Carboniferous sedimentary strata outcropping on the landward shore of the Worms Head Causeway at Rhossili show differential erosion by the sea. Some areas of the Black Rock Limestone Subgroup are clean, smooth and worn down whilst others are sharp and jagged with encrusting biofilms and barnacles. This is partly due to the varying compositions and relative hardness of the different strata, and partly to the way in which the waves with their rock-bearing loads seek lines of least resistance in the shore with each tidal ebb and flow. Areas of weakness, for example, between bedding planes and in minor faults with veins of soft white crystalline calcite and red haematite, are more vulnerable to repeated abrasion. This has led to the formation of numerous channels, gullies, and basins among other more resistant rock outcrops. Rounded pebbles and cobbles frequently lying within the hollowed areas evidencing their role in wearing the bedrock away. Mechanical abrasion allied to varying rock resistance is not the only way that the limestone is altered. Elsewhere on the causeway, limestone acid dissolution and marine organisms are the most common agents of natural change in surface texture and sculpturing, creating karstic and bio-karstic limestone topography.
5 Replies to “Water-worn Limestone 1”
Wonderful!: Your narrative, your photographs, the rocks.
Thank you, Linda. The rocks are special and so is the place.
As ever..wonderful photographs..you so capture the essence and character..I keep looking at them! Thankyou..inspiration!
Thank you for the feedback, Jan. I am very pleased that you like these photographs. I will soon be posting some more images from further along the same shore which exhibit erosion in a different way.
Topography is exactly it! Looked at from that angle, some of the images look just like aerial views.
LikeLiked by 1 person