Lead mining

Lead mining was once the main industry in parts of the Dales, including Wharfedale. From the seventeenth century to the late nineteenth it employed hundreds of men and boys, exploiting the veins in the limestone at Greenhow, Hebden, Grassington, Linton and Conistone, Appletreewick and elsewhere.

The smelting of the ore had a dramatic effect on the countryside. Writing in 1885, of the Grassington mines, Joseph Lucas said: "Formerly the hill-side, for hundreds of acres around, was destitute of verdure, as every green thing was killed by the poisonous vapours. No sheep or cattle could be safely pastured on the adjoining hill-sides, as the wind frequently carried the smoke long distances and affected everything on which it fell."

Later the introduction of long flues, reaching up the hillsides, within which the vapour could condense and from which pure lead could be recovered, improved matters: "The hill-side is green again"

The heaps of mining waste remain, contaminated with lead, and on which little will grow. The few plants that will are known as 'lead plants' - spring sandwort and alpine penny-cress.

Spring sandwort is characteristic of limestone areas, where it grows on scree, pavements and grassland as well as old lead mines. It requires reduced competition, and the bare spoil heaps suit it well. Its British distribution centres on northern England, on the limestone, but it is also found in north Wales, the Peak District, the west of Ireland and scattered areas of Scotland and England.

Unlike the commoner spring sandwort, alpine penny-cress is almost entirely restricted to rocks or soils enriched with lead or zinc. It is found on the lead spoil heaps and also river gravels, and, rarely, on outcrops of rocks which contain metals. Again, its main centre of distribution is in the northern Pennines. It can be fairly easily distinguished from other penny-cresses by its violet anthers. It does not actually require lead to grow - lead is normally toxic to plants, reducing root cell division, for example - but has developed an ability to grow there and to enjoy the reduced competition from other plants.

Some other plants have developed 'ecotypes' which can tolerate heavy metals, among them thrift and wavy-hair grass.

At Hawkswick Wood alpine penny-cress can be found on old mine spoil at the western end of the site. The numerous small-scale workings on Malham and Kilnsey Moors support both alpine penny-cress and spring sandwort. Spring sandwort is also to be found on the old lead spoil heaps around Greenhow and Hebden.