Cassington

About 7 km north-west of Oxford SP 465107

This pit is dug in the Floodplain Gravel, the youngest of the Pleistocene gravels of the Thames. The gravels are a composite depost. The lower parts are attributed to cold climate phases within the later mid-Devensian between about 40,000 and 26,000 years BP. Later parts represent a late Devensian aggradation between about 11,500 and 10,000 BP.

Bones may be found, specially at the base of the gravel, of reindeer, red deer, bison, horse and mammoth.

The gravel rests on Middle Jurassic Oxford Clay. The horizon exposed is the Jason Zone of the Lower Oxford Clay. The fauna of ammonites and bivalves occurs mainly as layers of crushed shells, but fine specimens, especially of ammonites, can be broken out of pyritic nodules. It was a series of these nodules that yielded the 5 metre long pliosaur now on display in the Museum court.

Ardley Quarry

near Bicester, Oxfordshire, about 19 km north of Oxford. SP 453256

The Middle Jurassic limestones and clays in this quarry were deposited as limey muds some 168 million years ago in a shallow sea. At that time the world was a warmer place and the site of Ardley lay at the latitude of modern north Africa. The area was a tract of mudflats and shallow lagoons fringing a shallow sea that stretched westwards into what is now the Cotswolds.To the north-east were the shallow swamps and the marshes of Northamptonshire. South-eastwards, towards London and beyond, was a low-lying land covered with forest and ferns.

The floor of the quarry is a massive limestone which is impressed with a large number of well-preserved dinosaur footprints in trackways up to 200 metres long. Most of these have now been buried by domestic waste, but two good trackways remain to represent the two types of dinosaur present. The first comprises three-toed footprints of a theropod, up to 70 cm long and two metres apart. The correct name for this trace fossil is Megalosauripus but the identity of the trackmaker may be Megalosaurus which is an appropriate size and occurs nearby in Oxfordshire in the slightly older Stonesfield Slate.

The second type is made up of prints like potholes, 60 cm across. They should be called Brontopodus but they correspond well with the feet of Cetiosaurus, bones of which have been found exactly at this level at several sites nearby in Oxfordshire.

Bones of these animals and casts of the footprints are on display at the Oxford Museum of Natural History