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Much of Headington is built around old limestone quarries. Only one good exposure of the limestones survive, at Rock Edge (formerly Crossroads Pit), at the junction of Windmill Road and Old Road.
The Wheatley Limestone has been quarried since the twelfth century and Oxford college records indicate its use as early as the thirteenth century. At first, the quarries at Wheatley supplied building stone to many Oxford colleges and to more distant localities such as Windsor Castle. However, after the end of the fourteenth century, new quarries at Headington became more important, and continued to be used into the early nineteenth century, by which time the poor weathering characteristics of the stone had been recognised. The earliest buildings were commonly constructed of 'random rubble' (undressed stone) or only partially dressed rock, often using Coral Rag. Later, sawn blocks of freestone from the Wheatley Limestone was used for finishing exposed surfaces or for entire walls.
The cliff has exposures of Upper Jurassic rock. There are many fragments of coral and fossils including sea urchins, and this pit is thought to have been a former boundary between a coral reef and the surrounding shallow sea. The south end has Coral Rag outcrops, and there is Wheatley limestone at the north end of the cliff.
Geological materials © NERC. All rights reserved. Topography © Crown Copyright reserved.
The geological exposures of the Upper Jurassic Coral Rag at this site enable geologists to reconstruct the environment 145 million years ago. During this period a warm shallow sea covered Oxfordshire, similar to that of the present day Bahamas Banks. At Rock Edge the Coral Rag is rich in fossil remains, derived from corals reefs that formed in the ancient shelf sea.
Oxford as it looked 145 million years ago.
Close examination reveals the presence of two types of limestone, reflecting the close proximity of the reef margin. One variety consists primarily of coarse fragments broken off the reef, whilst the other is finer grained, representing the lime sand that accumulated on the sea bed a short distance from the reef. Actual in situ reefs were previously visible in quarries located a few metres to the south.
Other nearby quarries (click image for larger version).
Magdalen or Workhouse Quarry
N 51° 45.632 W 001° 12.125
Last quarry to be worked
N 51° 45.357 W 001º 12.046
Wingfield Hospital North Quarry
N 51° 44.994 W 001° 12.551
Wingfield Hospital South Quarry
N 51° 44.894 W 001° 12.436
N 51° 45.060 W 001º 12.293
Traces can still be found at Slade Close. The flats are built inside the quarry, the outline of the quarry can be seen to the east and south of these.
The published coordinates will get you to the nature reserve, you will then need to explore to find the features. Parking is restricted for residents immediately adjacent to the reserve but you can park nearby on The Slade around N 51° 45.110 W 001° 12.327 or N 51° 44.972 W 001° 12.296. Either offer an opportunity to try and spot the quarry remains at Slade Close.
To log this cache please post a picture of yourself next to the cliff and a picture of a sign with this cache's name on it.