Bivalve shell

What’s an oolith?

This is a quite large and ornamented bivalve shell in which each growth line is beautifully preserved. The tiny ooliths that make up the Inferior Oolite limestone are also clear in the rock surrounding the specimen. These formed from grains of sand or shell fragments that were rolled around in the warm water, building up layer upon layer of calcium to form the egg-shaped oolith.

Horn Park Quarry near Beaminster is the smallest National Nature Reserve (NNR) in Britain, being just one acre or 0.32 hectares in size. It was once a working quarry but it is no longer and the remaining outcrop is protected by a fence. There is no collecting other than for scientific and educational purposes. A section of the fossil beds has been stripped back and protected from the weather by a removable cover. To arrange a visit, contact the Senior Reserve Manager on 07899 731404.


Find out more about bivalves on the molluscs pages.

Common name

Bivalve shell

Scientific name

Ctenostreon? pectiniforme? or rugosum?


Molluscs > Bivalves


Inferior Oolite

Time period

Middle Jurassic


174 million years

Where found

Horn Park Quarry

Found by

Bob Chandler


Beaminster Museum

Accession number