Kimmeridge Clay

Kimmeridge Clay, the lowest series of the Upper Oolite, consists of dark, bluish-gray shaly clay, which is sometimes bituminous and occasionally (as at Kimmeridge in the Isle of Pnrbeck) passes into a shale so rich in bituminous matter as to be used as a fuel. In other places the clay is calcareous, and contains nodules of argillaceous limestone or septaria. Near its base it sometimes shows sandy layers and clay ironstone. The series attains a maximum thickness of 600 to 660 feet.