Essex Geology

Introduction

Compared to most other parts of Britain the rocks of Essex and adjoining counties are young in geological terms. Even the oldest surface rock in Essex (the Chalk) is only about 80 million years old. Much older rocks are, however, present at depth (see ‘The Basement of Essex’). We have some idea about these ancient rocks because of the records of boreholes that have been sunk in search of coal and oil.

The surface rocks of Essex that were formed before the Ice Age (from the Chalk to the Red Crag) are described as the ‘bedrock’ or ‘solid’ geology. Much of this bedrock geology is concealed beneath the deposits left behind by glaciers and rivers during the Ice Age. The material laid down during the Ice Age is known as ‘Superficial’ or ‘drift’ deposits.

Cross section through the bedrock geology of Essex from Saffron Walden to Thurrock. Illustration taken from Essex Rock (1999).

For a geological timescale click here

For a summary of the main geological formations in Essex click here

For details of specific time periods in Essex geological history, click the links below:

Basement of EssexThe Chalk
Thanet Sand to Harwich Formation
London Clay & Bagshot Sand
The Red CragThe Early Ice Age
The Arrival of Humans
Formation of the Modern Landscape

Geological map of Essex showing all the rocks exposed at the surface – bedrock and superficial deposits. An example of a superficial deposit is boulder clay or glacial till left behind by the Anglian Ice Sheet during the Ice Age (shown in pale blue). Map based on published maps with the permission of the British Geological Survey.