Weald Clay is a Lower Cretaceous sedimentary rock underlying areas of South East England. It is part of the Wealden Supergroup of rocks. The clay is named after the Weald, an area of Sussex. It varies from orange and grey in colour and is used in brickmaking.
The un-weathered form is blue/grey, and the yellow/orange is the weathered form; they have quite different physical properties. Blue looks superficially like a soft slate, is quite dry and hard and will support the weight of buildings quite easily. Because it is quite impermeable, and so dry, it does not get broken by tree roots. It is typically found at 750mm down below a layer of yellow clay. Yellow, found on the surface, absorbs water quite readily so becomes very soft in the winter.
The two different types make quite different bricks.
Read more about Weald Clay: Paleofauna
Famous quotes containing the word clay:
“With earth’s first clay they did the last man knead,
There of the last harvest sowed the seed,
And what the first morning of creation wrote,
The last dawn of reckoning shall read.”
—Edward Fitzgerald (1809–1883)