8 Replies to “Porthmeor Rocks 3”

  1. Is the pitting (I don’t know what else to call it) in photographs 4a, 5a, 6a, and 7a due to inclusions being washed or dissolved out? Whatever the cause, the effect is beautiful. Thanks for catching it.


  2. Hi, Linda, pitting is a good word to describe it. I don’t think the pits in these rocks from Porthmeor mark the place where there used to be small inclusions. The surrounding rock seems to be uniform in its fine texture without inclusions. There are fine layers because this rock (as far as my memory serves me) is metamorphosed slate. The pits are probably due to a mixture of natural chemical and physical abrasion. The exposed rock face was near-vertical. The pits were not so apparent on the flatter outcrops. The burst-bubble texture may relate to internal softer and harder constituents of the rock that have given rise to uneven erosion. The same kind of weathering texture, often on a much larger scale, is quite common on beachside rocks I have photographed, including a type of basalt on the Oregon Coast, and boulders at Chapman’s Pool in Dorset. In limestone rocks like those at Doolin Quay in Ireland and Spaniard Rocks in Gower, the flat surfaces often have distinct circular pits caused by dissolution from acid water (rain and/or sea).

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