White chalk…
on John Calloway (Nepal), 04/Jan/2021 19:52, 34 days ago
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“The chalk that makes up Portsdown Hill was laid down between 100 and 65 million years ago at the bottom of a deep tropical sea. Chalk is made from the compressed skeletons of countless millions of marine algae called coccospheres. The same layer reappears to the north where it forms the South Downs, and again […]