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 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.
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.
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 e-mail me with the following
1) What material is at the south end of the cliff
2) Name the three main materials found on the cliff
3) Photo of yourself or GPSr in front of the information board
or the cliff.
Any logs without a photograph will be deleted