Horsham Stone is a type of calcareous, flaggy sandstone containing millions of minute sand grains and occurring naturally in the Weald Clay of south-east England.
The rock extends in an arc-like formation for several kilometres around the town of Horsham from which it takes its name, and lies just below the Weald Clay surface in bands 10 to 13 centimetres (3.9 to 5.1 in) thick.
[1] The fossil evidence in Horsham Stone and Sussex Marble indicate a diversity of life living on a broad, flat subtropical landscape.
Towards the end of the Cretaceous period around 90 million years ago, most of Britain including Sussex would have been submerged beneath a tropical sea that was depositing chalk.
In later centuries there are numerous examples in Sussex and the surrounding counties as a roofing material, particularly for mills, dovecotes, churches, manor houses and similar buildings.