One of the outstanding and peculiar geological features at Osmington Bay is the presence of huge, strange, rounded, smoothed boulders with a part division along the equator that makes them look like giant burger buns! The rounded shape is similar to water-worn pebbles – but on a larger scale.
As you can see from the pictures above and below, some of them are very big – well over a metre in diameter. For an idea of scale, the guy in the photos is nearly 2 metres tall.
These huge boulders started off in a layer at the base of the cliff. There are still many in position there. They gradually fall free of the surrounding softer rock by a combination of weathering and wave action. These boulders are in fact “nearly spherical carbonate-cemented sandstone nodules” of Bencliff Grit which belongs to the Upper Jurassic Corallian Formation Beds.
The nodules in various stages of breakage are scattered quite widely over a large section of the beach. You can hop from one to the other which is easier than walking over the other smaller boulders.
These boulders are really spectacular. Their geological origin is a bit complex. So I suggest that if you want to get a more detailed explanation, have a look at Ian West’s excellent web site on the geology of Osmington Mills.
A row of these large Bencliff Grit nodules is partially exposed in the lowest part of the cliff at Osmington. The picture above gives a view looking westwards towards Weymouth.
This photo shows the view of the Bencliff Grit nodules looking east towards Ringstead.
This specimen is standing on a pedastal of the softer rock matrix. When the waves erode this away, the nodule will fall onto the beach to join the others. These nodules are also called “doggers” in geological terms. The last picture is for scale: my walking pole is leant against the embedded nodules in the cliff.
Revision of a post originally published in July 2009
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