Fossil oyster shells (Deltoidium or Liostrea delta) from the Upper Jurassic period are commonly found on the seashore at Ringstead Bay in Dorset. Dating from over 135 million years ago, these fossils can easily be seen protruding from the grey sticky clay that forms low crumbling cliffs at the top of the shore. This clay is known as the Ringstead Waxy Clay. Sometimes the oyster shells wash out after heavy rains and winter weather. In the photograph below you can see some fossil oysters end-on in situ, with the edges of the shells visible in the clay as it dries out in the early spring sunshine.
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Jessica's Nature Blog 
Hello, I am an artist that lives in new Orleans, La. recent site of Oil Spill in the Gulf of Mexico. I come from a long line of Croatian immigrant oyster fisherman and then Mississippi River boat pilots. Our recent spill event has destroyed our coastal reefs and oyster economy. I have a re-newed interest in my heritage and the culture of oysters in general. Your wonderful site has been the most informative source of information about the natural history of oysters to date for my research. I have found a source in the city of very old (?/midden) oyster shells that are beautiful, free form and have an amazing golden patina. They are in a semi-industrial area and its seems they have been protected by circumstance for a long time. Thank you so much for all the information about Oysters. Your Blog has helped me to understand how old they might be. I will be having an exhibit this March and studio photographs of these jewels will be included. The web-site posted is my gallery here in New Orleans and I am represented /scroll down/ for bio.
Krista Jurisich
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Thanks for getting in touch, Krista. Nice to hear from you. Sad to learn how the local oyster industry has been affected by the oil spill. I hope that it will not be too many years before the oyster populations recover. The archaeological record in Great Britain seems to suggest that oysters have passed through cycles of abundance followed by periods when they are not apparently available for exploitation at all. In these historical instances it would be natural changes – such as disease, climate change or just successive cool summers that could probably have affected oyster population mortality – before favourable circumstances return and promote active recruitment to the oyster beds again. Oysters have been around for many millions of years as evidenced by the fossil record as well as the archaeological. They are real survivors. I hope conditions stablise quickly in the Gulf of Mexico to permit a speedy return of oysters to your reefs.
I have had an interest in the causes of variations in oyster shells for most of my adult life. I have examined many thousands of oyster shells uncovered during excavations of historical sites. I have, like you, come across shells with a golden patina. This has sometimes appeared to be an actual thin coating of substance that has accreted during burial – especially in ancient rubbish pits. I have not analysed the composition of the coating but think it is caused by mineral-laden water permeating the shell deposits. In other cases, a slightly iridescent golden colouration of the shells (rather than a coating) has been caused by burning – as in shells that have been discarded in fires after the oysters have been opened by roasting in hot ashes.
I am pleased that you found my articles on oyster shells useful.
I look forward to seeing your artwork with photographs of the shells in your forthcoming exhibition.
Jessica
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