Geology Site Account

Site name: Mill Wood Sand Cliff (part of Chafford Gorges Nature Park)

Grid reference: TQ 5943 7872

Brief description of site:

Cliff of Thanet Sand laid down in a tropical sea 60 million years ago. A site of geological interest with potential for geological education. Part of Chafford Gorges Nature Park.

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Site description

In 1872 Gibbs and Company Ltd established a cement works west of Mill Lane. This was one of the first cement works on the Essex side of the Thames and is notable for the experimental use, in 1887, of the rotary kiln that was subsequently used successfully in cement works around the world. The quarry was called Mill Wood Pit or Gibbs Pit but it was also known as Thames Works Quarry. It produced many fine fossils to generations of collectors, mostly sea urchins or echinoids exquisitely preserved in flint. In common with other quarries in the area, the chalk of Mill Wood Pit is capped with a thickness of Thanet Sand and, at the very top, a layer of Orsett Heath Gravel laid down by the early Thames.

After closure of the cement works the quarry became a haven for wildlife for many decades, particularly for a number of nationally rare invertebrates. Despite this biodiversity the quarry was sadly lost to housing but there is still a small amount of geological interest remaining at the north end of the quarry in the form of a cliff of Thanet Sand. This can be accessed from Saffron Road, or from Mill Lane via the footpath between the top of the cliff and Mill Wood and then down a flight of steps to a grassed area at the bottom of the cliff. The cliff provides an excellent opportunity to examine the Thanet Sand, sand that accumulated on the edge of a shallow sea some 60 million years ago. Scientific examination of the sand grains has shown that most of the sand originates in Scotland and has been brought south, over several million years, by coastal currents. At the very base of the cliff is the junction with the underlying Chalk but it has been obscured by fallen sand.

At the top of the cliff are occasional glimpses of the gravels of an ancient route of the Thames, which appear to have been channelled down into the Thanet Sand by the action of running water. The gravel is easily visible from the wooden steps. It is known as Orsett Heath Gravel and is now about 30 metres (100 feet) higher than the present river. It is from the highest and oldest of the Thames terraces and is about 380,000 years old.

This cliff section forms part of Chafford Gorges Nature Park and is managed by the Essex Wildlife Trust. Elsewhere in the park similar sections can be seen in Lion Pit, at the south end of Warren Pit and at the Sandmartin Cliff.

Thanet Sand overlain by iron-stained Thames gravel (Orsett Heath Gravel) at Mill Wood Sand Cliff. Photo © G. Lucy