Oxford Clay

Oxford Clay, a rock belonging to the Middle Oolite or lower part of the Upper Jurassic, generally dark-blue, containing some lime, much pyrites and selenite, and many septaria (q.v.), is from 300 to 600 feet thick, and extends across England from Weymouth, through the Vale of Blackmore, to Chippenham, Oxford, Huntingdonshire, and under the Fens to Hackness and Scarborough. It was also found in the sub-Wealden boring near Battle, in Sussex, from 950 to nearly 2,000 feet below the surface. It is often worked for brick-making. Besides ichthyosaurs and plesiosaurs, the most characteristic fossils are the bivalves Gryphaa dilatata and Trigonia clavellata, and the cephalopods Belemnites hastatus and Ammonites Elizabethan.