Geology Site Account

Site name: Gravelhill Wood, Langdon Hills

Grid reference: TQ 6775 8637

Brief description of site:

The Langdon Hills straddles the boundary between the districts of Thurrock and Basildon. This high ground is capped with Bagshot Sand and the enigmatic flint gravel known as 'pebble gravel', the origin of which is not fully understood. There are panoramic views over the present Thames Estuary and across to London.

Gravelhill Wood, southwest of the church, contains at least two large and obvious gravel pits, very overgrown, but with plenty of gravel visible here and there, especially where trees have toppled over or badgers have been at work. Gravel is also showing in the banks on the side of the adjacent Old Church Hill.

Gravel Hill car park is on the edge of the wood.

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Site details:

The Langdon Hills are composed of an isolated patch of Bagshot Sand overlying Claygate Beds and London Clay, and the summit, like other similar high points in the area, is capped with flint gravel. The Bagshot Sand and the overlying gravel were formerly visible in several small pits in the area.

The Bagshot Sand, Claygate Beds and London Clay were formed on the floor of an sub-tropical sea some 50 million years ago but the gravel at the very top of the hill is clearly much younger and of a different origin. Originally known as pebble gravel, and called Stanmore Gravel on modern geological maps, this gravel was for years thought to have been laid down under a sea but it is now thought that it may have been deposited by a river. But how could river gravel, of geological recent origin, be capping the tops of some of the highest hills in the region?

For many geologists the riddle of the pebble gravel has now been solved by studying the pebbles it contains. Although mostly of flint, a small proportion are distinctive pebbles of chert from the Lower Greensand of The Weald, and other rock types that could only have been deposited by a river flowing from the south. Similar gravels are found capping the high ground in Epping Forest and the Rayleigh Hills. These isolated outcrops of gravel date from the early part of the Ice Age, perhaps as much as a million years ago, and were probably laid down by northward-flowing tributaries of the Thames, when the Thames flowed across north Essex and Suffolk before its diversion to its present course by the Anglian ice sheet 450,000 years ago.

It is difficult to believe that this gravel may originally have been the floor of an ancient river valley. Curiously this gravel may even be the reason these hills are here, the gravel protecting these parts of Essex while the surrounding land was reduced to the present lowland by hundreds of thousands of years of erosion.

Although only partly within the district of Thurrock the Country Park is run by Thurrock Councils Ranger Service.

Pebbles of flint from the Pebble Gravel (Stanmore Gravel) in Gravelhill Wood. (Photo: J. Saward)