Geology Site Account

Site name: Margaretting railway cutting

Grid reference: TL 682 023

Brief description of site:

Railway cutting in the 1840s exposing a fine section in the London Clay, Claygate Beds and overlying boulder clay (till). The section was studied by the distinguished geologist Joseph Prestwich who also collected fossils from here, some of which are in the Essex Field Club collection. The first scientific record of the fossil bivalve Venericardia trinobantium was from this cutting. This site is therefore the type locality for this species.

Details

When a layer of sedimentary rock is found in two different places it is not possible to establish that it is the same rock by its appearance alone. William Smiths discovery that each layer contains distinctive fossils was therefore crucial to correlating sedimentary rocks in different parts of the world. Sometimes a single fossil may be the only way to distinguish each layer.

In Essex, a good example of this is a fossil bivalve or cockle with the rather unnecessarily long name Venericardia trinobantium. This fossil (which is named after an ancient Essex tribe Trinobantes, who fought the Romans with Boudicea) is very useful to geologists as it only occurs in the Claygate Beds (the sandy clays at the top of the London Clay). It was very common, and appears to have lasted only a few hundred thousand years before becoming extinct.

The first scientific record of this fossil was from Margaretting, found in 1843 by the distinguished geologist Joseph Prestwich (1812-1896) during construction of the railway cutting. Prestwich worked in the family wine merchant business for 40 years and his geological research was carried out in his spare time; and it was during these off duty moments that he visited Margaretting. He was eventually knighted and became professor of geology at Oxford University. His large collection of British fossils, which included many from Margaretting, was donated to Londons Natural History Museum but several examples of the molluscs from Margaretting are in the Essex Field Clubs geology collection.

In addition to exposing the Claygate Beds and the London Clay, the cutting provided a fine exposure of boulder clay left behind by the Anglian ice sheet.