Geology Site Account

Site name: Harts Wood

Grid reference: TQ 603 923

Brief description of site:

Potential exposures of Warley Gravel and Bagshot Sand in ravines or stream banks and in the roots of fallen trees. Harts Wood is owned by Brentwood Council and accessible at all times.

----------------------------------------

Details

The bedrock of Harts Wood consists of Bagshot Sand. This formation is as a result of the gradual shallowing of the London Clay Sea about 50 million years ago. The sediment being deposited on the subtropical sea floor started as a mud that we now know as London Clay and became more and more sandy until eventually it consisted entirely of the fine yellow sand we now call Bagshot Sand. This sand was probably laid down across most of Essex in a great complex of river deltas and all that now remains of it are isolated patches on the tops of these hills in south Essex, the rest having been removed by the intense erosion of the Ice Age.

On top of the Bagshot Sand in this area is an extensive spread of Warley Gravel (called Stanmore Gravel on modern geological maps), which dates from an early period of the Ice Age and may be over a million years old. The origin of the Warley gravel is unknown, but one theory is that it was deposited by a south bank tributary of the early Thames when the Thames flowed across central Essex. Numerous rounded pebbles from this gravel can be seen in the wood.

See the site account for Holdens Wood in Great Warley for more information about the Warley Gravel.