You can see from this picture how the Sunburst Lichen got its name. The yellowy-orange folds and corrugations radiating out in concentrically arranged circles of subtley changing hues, make Xanthoria parietina a striking coloniser of the rocks above the high water mark – where the limestone is most frequently merely splashed by the waves rather than submerged for long periods beneath them. Smaller irregular encrustations of deeper orange coloured lichen called Caloplaca marina spread out around it on the pale grey Carboniferous limestone of Spaniard Rocks at Rhossili on the Gower Peninsula.
Lower down in the intertidal zone where the rocks spend longer under water, the black lichen Verrucaria maura coats the stone of extensive areas. Its dark thin crust and cracked surface from a distance looks like dried oil spill deposits. Its mottled patchy patterns against the pale rock are conspicuous. Cream-shelled acorn barnacles of various species dot and cluster in crevices amongst the lichen – adding to the naturally occurring designs.
At low tide level, frequently-submerged areas of limestone become worn smooth from the constant battering of the surf with its load of sediments and flotsam; and apparently dissolve away to form extraordinary hollows and basins retaining tide-pool habitats when the sea recedes.
At high tide level the limestone remains stark and angular. In places the break-up of the strata resembles a series of steps whose angles are accentuated by the low winter sun illuminating the risers and casting shadows across the treads. Elsewhere the splits and clefts in the stone surfaces create geometrical patterns like inter-connecting triangles.
Spaniard Rocks is an exposure of Carboniferous limestone which lies at the northern end of Rhossili Bay in Gower. It is separated from the small island of Burry Holms by a narrow causeway that floods on the incoming tide. It underpins the northern part of the stabilised sand dune covered Llangennith Burrows.
Revision of a post first published 20 March 2010
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