Kimmeridge Bay: the Kimmeridge ledges

The little Purbeck village of Kimmeridge has lent its name to a late stage in the geological Jurassic period, the Kimmeridgian, and also to the unhelpfully named Kimmeridge Clay.

Kimmeridge Clay is of course not clay but rock: a rock stratum which harbours a wide variety of fossils including those of sauropods, plesiosaurs and ichthosaurs. In addition, it is the most important source rock for North Sea oil.

In this photo you are looking at one of the several Kimmeridge ledges, which stretch out into the English Channel. In the background is the Clavell Tower.

Kimmeridge Bay is home to a number of local fishermen. Because of the presence of the ledges, navigating into and out of the Bay is a precise art and hazardous to anyone who does not know the Bay well.

This black shale is a surface outcrop of Kimmeridge Clay, and variously known as Kimmeridge Oil-shale, Kimmeridge Coal or Blackstone. Various attempts have been made to use it as an industrial fuel. It is bituminous and, when burned, gives off a sulphorous smell. The shale's propensity to catch fire spontaneously is another of its unfortunate attributes.

Sir William Clavell (1568-1644) of Smedmore House used the shale both for the production of alum and at the same time as the fuel to produce it: alum has numerous industrial and cosmetic uses, and since Roman times has been used for purifying drinking water. However, the alum production infringed a monopoly in the product granted by the King, and had to be closed. The enterprising Sir William then turned his energies to using shale for the production of glass and salt.

In Roman times the shale was used for the production of armlets.