One rainy morning I walked the coastal path along the terrace at the foot of Rhossili Down in Gower. Clouds shrouded the slopes of the Down above me. Ahead of me, Burry Holms and Llangennith Burrows were part concealed by mist. Below me, the tide was going out – far out. The sand on the beach was still wet from the waves and the rain. Slowly the cloud cover thinned and allowed a filtered light to penetrate. The pale light was reflected by the shore, high-lighting the sea-sculpted rows of ridges and ripples in gentle gleaming silver. A stream cascading from the height of the Down worked its way down to the beach, where it spread out in a fan of interweaving channels that cut across the parallel ridges on its way to the water’s edge. Coloured sediments carried by the stream tinted the silvery patterns and made them seem opalescent.