It takes its name from tiny particles of a polymer that can be injected with water into oil-bearing rock strata.

These would force it down boreholes into rock strata lying up to three miles beneath the seabed.

Supporters of fracking argue that it can access vast supplies of natural gas lying locked in underground rock strata.

The rock strata are almost vertical, and the bands of rock are quite narrow.

Rain water and pooled water from ponds, lakes and rivers percolate through the soil horizons and the upper rock strata, thus becoming groundwater.