Geoscience Reference
In-Depth Information
F
IG. 66
Plot experiments for establishing vegetation on sand wastes from china clay workings in Cornwall. (Pho-
tograph R.H. Marrs.)
The mountains of deep-mined shale which used so to dominate parts of the land-
scape of south Lancashire, Yorkshire, Northumberland and Durham presented a great-
er range of problems for vegetation establishment than the china clay tips. These
heaps could be up to 200 ft (65 m) high with slopes as steep as 35° and littered with
many coarse fragments the size of dinner plates. Apart from their instability and tend-
ency to erosion, many of the tips showed persistent toxicity resulting from the ex-
treme acidity of the shale. The pH of some types of shale could be as low as 1.5-2.0
owing to the presence of iron pyrites. Chemically, this mineral is iron sulphide (FeS
2
),
which was formed under anaerobic conditions in the swamps where the original Car-
boniferous deposits were laid down. When iron pyrites occurs in large crystals, it
has a golden colour from which it has gained the name of 'fool's gold'. More often,
however, it occurs in coal shale as tiny strawberrylike granules - framboidal pyrites -
in which state it is highly reactive towards oxygen and water.
TABLE 12
Soil profile on a coal shale waste heap after 100 years. (From I.G.Hall 1957)
