Geology Site Account

Site name: Audley End House Septarian nodule

Grid reference: TL 5220 3828

Brief description of site:

Half of a local septarian nodule is on display in the Stable Block of Audley End House. It is thought that it was found locally on the estate in the 19th century.

Details

On display in the Stable Block of Audley End House is a splendid septarian nodule cut in half to display the internal cracks lined with calcite crystals. It is 1.65 metres x 1.15 metres (56 x 40€) in size and was moved from its previous position on the Tea House Bridge in 2003 to deter vandalism.

This remarkable nodule, or concretion, is a rock that was formed in the mud on the sea floor during the Jurassic period, about 160 million years ago. This mud eventually became the Jurassic clay that now forms the landscape between Peterborough and Bedford. Nodules such as this are frequently encountered during road widening or similar excavations. Over millions of years the nodules dried out and as they did so they would shrink from the centre outwards, forming a network of cracks which filled with crystals of the mineral calcite. The cracks are called 'septa' which gives them the name septarian nodules. This particular example has been sliced in half to reveal the internal structure.

The history of this nodule is unclear. It is thought to have been part of the natural history collection that was accumulated by the fourth Lord Braybrooke in the nineteenth century and it is likely to have been obtained by him from one of the brick pits then in operation in the Saffron Walden area. These nodules occur in Essex as a result of being transported south from Peterborough by an ice sheet during the Ice Age, about 450,000 years ago.

Audley End House is an English Heritage property. The rest of Lord Braybrookes natural history collection, which includes a mammoth tusk collected nearby in 1832, can be seen inside the house.

The Audley End septarian nodule. Photo: G.Lucy