Old Pasture lime kiln, Conistone: The unusual structure on the Dales Way which was vital for Yorkshire's farmers

Today at least 130 have been identified and kept in various stages of preservation. In the fields around Keld in Swaledale there were as many as eight kilns.

This one at Old Pasture above Upper Wharfedale, between Grassington and Conistone, is among the best known as it is on the route of the Dales Way.

A metal plaque next to it states that it was built about 150 years ago.

Here, as at the other small kilns, a layer of kindling was placed at the bottom and layers of limestone and coal loaded into the top.

After the kindling was lit, the limestone was left to burn for three days, the arch at the front drawing air into the kiln to keep the fire burning.

The resulting lime was raked out at the bottom through a small hole called the “eye”.

The Old Pasture kiln is privately owned and was subject to conservation work in 1994.

The production of lime eventually became a sizeable commercial operation in the limestone areas of Craven.

In 1873, a huge kiln was built north of Settle in Ribblesdale with 22 firing chambers.

Known as the Hoffmann Kiln after its German inventor, Friedrich Hoffmann, it burnt blocks of limestone quarried from nearby Langcliffe Scar.

The lime was sold as fertiliser to farmers, and also to builders for use in mortar and to local industries like tanning, textiles and paper making.