Oyster Day - an article from The Illustrated London News.
"August 4 was, in metropolitan parlance, "Oyster Day", i.e. the day on which oysters are first brought into the London market at Billingsgate.
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There were fifty sail of vessels at market from Rochester, Whitstable, Essex, and the Cheyney rock, near the Isle of Sheppy.
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Date: 12 August 1843