Formed between 340 and 342 million years ago, it is believed to have been the site of a deep Carboniferous lagoon measuring approximately 50 kilometers across. Outcrops are visible in and around Edinburgh, Scotland. The formation is known for its siderite concretions containing fish and coprolites. (Alister Cruickshanks, UKGE Limited and Geological Conservation Review, Vol. 16, Chapter 9). For more information see http://jncc.defra.gov.uk/pdf/gcrdb/GCRsiteaccount1370.pdf
