The greater part of the cliffs on Monmouth Beach at Lyme Regis in Dorset, UK, on the Jurassic Coast, are made up of the Blue Lias sediments laid down in the Lower Jurassic Period. They are composed of alternating layers of hard pale limestone and softer, finely-bedded, shales and mudstones. The rocks of the cliff face are rapidly eroding back. Wave action and weathering wear away the softer layers so that the harder rocks above them are no longer supported and this leads to frequent falls of the stone down to the shore below.
The rock strata stretch out horizontally from the base of the cliff and extend seawards as a hard limestone rock pavement. This platform is also subject to wave action that breaks it up – resulting in a series of wide steps across the seashore in some places. These steps reveal the layering of the different strata, echoing that seen in the cliffs. Thinly layered, dark, soft rocks are sandwiched between lighter-coloured more resistant ones. Whilst the horizontal surfaces of hard limestone form the ‘treads’ of the steps, the softer, darker, shaley rocks form the ‘risers’.
The photographs in this post illustrate the junction between the two rock types on the beach – the edges of the ‘steps’. Viewed from above, with midday sun casting strong shadows, the contrasts in colour and texture are emphasised. The natural pattern made by the cracking and delamination of the layers of rock assumes an abstract graphic quality.
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