RECLAMATION AND RESTORATION - The Soil - page 204

This proto-soil had also become colonized by five kinds of earthworms, notably
by Lumbricus terrestris whose presence was often betrayed by small aggregations of
stones that had been dragged towards its burrow (see chapter 5 ) . Their biomass was
not inconsiderable, and they would be important agents in the incorporation of dead
vegetation below ground. A few small snails and some hardy kinds of soil arthropods
were also present, especially the drought-resistant oribatid mite Humerobates rostro-
lamellatus and the pill woodlouse Armadillidium vulgare , contributing to the break-
down and cycling of plant material.
Older parts of this quarry, and other chalk and limestone quarries, show how
such pioneer communities can help to develop a closed grassland turf not unlike that
found on thin Rendzina soils of the chalk downs or upland limestone pastures. Some
quarries become colonized by shrubs and trees whose roots penetrate more deeply,
fissuring the rock, bringing up nutrients, and enriching the lower soil horizons with
organic matter when they die. As vegetation covers the ground, it acts as a protective
blanket, reducing the destructive effects of wind and rain as well as the extremes of
temperature to which the bare surface was exposed ( Fig. 65 ) .
Increasingly, today, such old quarries are either reworked or used as receptacles
for spoil or domestic waste. The problem of restoring vegetation on such landfill sites
is dealt with later. It is worth noting, though, that certain quarries are important out-
door museums for their geological exposures, while some naturally colonized quar-
ries are interesting and attractive places in their own right simply because of their im-
mature ecosystems.
Many kinds of plants may participate in this colonization process in chalk and
limestone quarries because, although there is a deficiency of nitrogen, phosphorus and
potassium, there is often an abundance of magnesium, iron and, above all, calcium
in the rock. Where calcium and magnesium are also lacking in the parent rock, as in
granite, vegetation has a still greater struggle to become established. This situation
occurs in the abandoned waste tips of the china clay industry in Cornwall, for these
are derived from the granite cores of ancient volcanoes. China clay, or kaolinite, is
itself an extremely pure and fine material (an aluminium silicate, see chapter 1 ) . It is
washed out from the decomposed granite leaving vast quantities of quartz particles,
with a certain amount of mica and clay, in the older workings. This waste material
cannot be put back into the holes, for they are virtually bottomless as far as the in-
dustry is concerned, so it is heaped into giant sand castles.
Not only do these wastes contain extremely small amounts of all the major plant
nutrients, but they often lack even the basic minerals from which such nutrients could
be derived. Natural plant colonization on these tips is therefore a very slow process,
and is closely linked to the accumulation of nutrients from the air. The spoil receives