Geology of London

On top of these clays is a non-contiguous layer of Upper Greensand above which lies a rolling bed of white chalk about 200 metres thick.

Most significant is the stiff, grey-blue London Clay, a marine deposit which is well known for the fossils it contains and can be over 150 metres thick beneath the city.

Southern England at this time was covered by a warm tropical sea: this is shown by the fossil evidence.

This was deposited during the last ice-age ½ million years ago when the River Thames was diverted to its present position.

While establishing its new path, the river eroded its valley, creating a series of sand and gravel terraces.

In places, there are deposits of brickearth, which is a mixture of clay and sand that has supported London's long-standing brick-making industry.