From a plaque next to the kilns:

Under tremendous heat, rock-hard limestone was transformed into powdery-fine lime in the lime kilns that you see. Limestone, first quarried and later mixed, was brought from vast deposits on Lincoln Hill, which rises behind the kilns. Though lime kilns have been found in the Gorge since medieval times, these kilns operated from about 1760 to 1870 when Lincoln Hill supplied huge quantities of limestone to surrounding iron furnaces. The best stone no, doubt, was sent to the furnaces and the lower grade stone was used to make lime.

The continually burning kiln was charged from the top with alternating layers of limestone and fuel, usually coke. The kiln often burned for a week or more to convert the limestone into lime. Under the intense heat of the kiln, carbon dioxide was driven off from the limestone to produce lime.

As the Kiln burned, lime clinker fell through the draw hole at the bottom of the kiln and more fuel and limestone were added at the top. The clinker, large lumps of lime, was then slaked with water. The lumps of lime absorbed the water, expanded, and crumbled into a fine powder. The lime was then ready to be used by builders for mortar, and farmers as fertiliser.