An early Tertiary (60-40 Mya) volcano forms the core of the Cornelian Bay Cemetery site, and basalt from it is exposed in the cliffs there. Gemstones (cornelians) have been washed out of basalts onto the adjacent mudflats. [‘The semiprecious gemstone cornelian/carnelian is a variety of the silica mineral chalcedony , coloured by impurities of iron oxide. The colour can vary, ranging from pale orange to an intense almost-black coloration ‘(Wikipedia)]. Behind the Cornelian Bay boat-sheds, a jumbled sequence of landslide material (sandstone melee) contains large fragments of the freshwater carbonate mineral travertine. Charles Darwin visited this site in 1836 and considered the travertine to have ‘originated in a spring deposit (further uphill) which was later disrupted by a mass-flow down the slope of an ancestral Knocklofty’ during earthquake/volcanic instability in early-Tertiary time. Nearby, older layers of pudding-rock conglomerate occur, formed during volcanic activity.
1854 map of cemetery area, showing volcano outline, from Fig 8 in A Tranquil haven: a history of Cornelian Bay, Lindy Scripps, 2006; Sketch below by Pat Martin, 2024
Cornelian Bay cornelians - note their orange colouring
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