The Worm’s Head Causeway at Rhossili in Gower is a dramatic geological feature – a jagged rock platform carved by the sea across an ancient fold in the strata. What remains is a landscape of angled and upstanding, differentially-worn rock layers arranged in row after row.
The photographs in this post show water-worn smooth layers of Carboniferous limestone. This rock is mostly grey but some whole areas are coloured pink – and where the rock remains wet in the cracks and fissures, the pink hue is enhanced and appears red.
Additionally, in a few rock crevices, there is a distinct streak of deep red sediment. These deposits could possibly be the result of one of two phenomena. Some veins in the Carboniferous limestone contain calcite and haematite. Heamatite is a form of iron. According to one account of Gower geology
The blood-red haematite ore was probably derived from the underlying Old Red Sandstone by the action of hydrothermal solutions from which the vein minerals were crystallised.
(Jonathan Mullard (Gower, New Naturalist, Collins, 2006 ISBN -13 978-0-00-716066-6)
Certainly there are deep red sediments associated with white crystals in other locations nearby on The Causeway. I’ll post some pictures of those shortly.
Maybe there is an alternative suggestion for the origin of the red sediments in the limestone fissures, especially where they are not accompanied by calcite crystal. Rather than being an intrusion into the rock by solution from older Devonian rocks below, I wonder if they might be infills of red ochre from younger Triassic rocks which once lay above the Carboniferous Limestone. Complex Triassic sediments, like red ochre, are known to penetrate downwards to infill fissures in the Carboniferous limestone below. This has been recorded in the Port Eynon region further round the Gower coast – although I am unable to find a reference to red ochre occurring in the Causeway rocks.
From a distance, the rocks look like they are bleeding.
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