An artists' impression of the Jurassic sea bed at the time
of the formation of the Portland Stone

From The Ecology of Fossils, by Dr Swart McKerrow as Editor, Pub. Duckworth. 1978
By permission of the authors.

Key

a.
b.
c.
d.
e.
f.

Ostrea - The oyster (Liostrea)
Calcareous algal mound (Solenopara)
Boring bivalve, burrowing into the algea (Lithophaga)
Ostrea - a small curved species (Isognomon)
A fossil Top-shell: a marine snail  (Pleurotomaria )
A tall spiral marine snail (Protocerithium)

Calcareous algae are rubbery mats which trap fine lime sand and partly precipitate calcite (lime) from sea water. The algae has no internal structure as such and no tissue is fossilised.
Pages 10-11

Pages 13
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