The Bargain Stone EarthCache

There are two large pieces of stone in prominent positions in Harwell High Street. The more southerly stone is often referred to as the Bargain Stone or Bidding Stone, a name thought to derive from times when horse fairs were held in the village and deals struck at the point where it was located. It is thought that the stone was moved to its present position from land in front of the barn that used to be on the corner of Kings Lane and High Street, the barn being an outbuilding to Adnams Farm. The other stone is indicated here as a waypoint and is the site of a separate cache (GC32X3A, by MissMarkey). Further examples of Coral Rag stones used as barn footings can be found at the Cherry Barn (in the High Street) and at the barn on the corner of High Street and Grove Road (also a waypoint here).

Both stones are made of a rubbly limestone composed of ancient coral reef material and called Coral Rag. It is possible that they came from Abingdon Abbey around the time of its dissolution in the 16th century. The Abbot and monks signed a deed of surrender to the Crown on February 9th 1538, after being assured of decent pensions. John Wellsbourne, the King’s man in charge of winding up the Abbey’s affairs (it is estimated that it was the sixth wealthiest in England at the time), found that the Abbey had been stripped of all its furnishings: the community had made careful preparations for the surrender! Within weeks the Church was dismantled and all the good quality building stone barged down theThames. Hence, one can assume that the pieces in Harwell arrived soon after this date. Maybe this piece was thought not to have been good enough for barn footings.

If you look carefully at the stone you can see imprints of fossils. However, there are better examples in the wall of Cherry Barn, near the entrance, with remains of the coral being clearly visible.

The stone was almost certainly quarried from the Corallian Ridge, a distinctive landform feature running from north Wiltshire across to the east of Oxford, with well-known high spots at Badbury Hill and Faringdon Folly. Near Faringdon, the ridge is known locally as the Golden Ridge. The thickness of the ridge is usually estimated to be only 100 feet or so, although a sequence near Harwell was measured in 1985 at 250 feet thick. The ridge is characterised by woodland, including a significant proportion of ancient woodland; country houses in gardens designed to look out over the north-facing scarp; limestone villages built of local coral ragstone and expansive views to the north, south and, at the Oxford Heights, to the east. The soils tend to be light and sandy, with large arable farms to the west. The sands which form the heaths around Frilford are part of the Corallian landscape.

The Corallian outcrop has been extensively quarried for both sand and building stone and many of the ancient buildings in Oxford, as well as parts of Windsor Castle, are built from the Coral Rag and Wheatley limestones. Quarrying continues to this day for building sand, gravels and aggregates.

Corallian rocks date from the Jurassic period (from 199.6 to 145.5 million years ago), having been deposited on top of the Oxford clay and some time before the Greensand and chalk deposits well known in the area (these can be seen clearly just to the south of Harwell village, where the land rises from the A417). The Corallian consists of a varied sequence of sandstones, clays and shallow marine limestones with local developments of coral. The nature of the deposits suggests that they formed relatively close to a shoreline. Much of the Corallian Group is richly endowed with fossils, containing corals, gastropods, bivalves, echinoids and ammonites. Some of these can be seen in the two stones in Harwell and examples are shown in the following diagrams.

The Corallian has been broadly divided into the Lower Corallian and the Upper Corallian divisions. The Lower Corallian is represented by the sands and hard, chalky sandstones of the Lower Calcareous Grit Formation. This formation consists of yellow and white sands and sandstones, containing bands of hard, round masses or 'doggers'. The Lower Corallian is succeeded by a jumbled sequence of shelly, fragmented limestones, which include coral debris, sandstones and mudstones, and which together comprise the Upper Corallian division. The top of the Upper Corallian is known as the Coral Rag Formation and contains reef-building corals that, in places, form irregular blocks three feet or more in diameter. The Coral Rag was deposited onto a variety of underlying Corallian strata, depending on the location. In some locations, the formation was deposited directly onto the eroded surface of the Lower Calcareous Grit.

Reference material for this cache description has been taken from several publications, including:
- British Geological Survey commissioned report CR/04/262N, "Baseline Report Series: 14. The Corallian of Oxfordshire and Wiltshire" (including the geological map)
- The chapter on geology in "Harwell - village for a thousand years" by Martin Ricketts, available at http://www.village4a1000years.com/the-geology-of-harwell-parish/ (including the background image to this cache page)
- Various sets of minutes from Harwell Parish Council meetings

The Bargain Stone has a distinctive hole at the bottom, through which dealers are rumoured to have sealed a sale by shaking hands. It would be fun to see pictures of you shaking hands through the hole when visiting this earthcache.

In order to claim this cache, please answer the following questions through our profile (some preparatory research may be required):

1. Examine the Bargain Stone and decide whether it is a rough piece of stone or has been worked for building purposes. Explain your reasoning.
2. What evidence of fossils can you see in the Bargain Stone? Describe their appearance and size. Alternatively, you may examine the stones at the Barn waypoint and answer the same questions for them.
3. How many million years ago do you estimate that the rock stratum was deposited from which the Bargain Stone was quarried?
4. Just make sure you are at the correct location, there is a triangular manhole cover a few feet to the south of the Bargain Stone, with a number displayed on it. Please tell me the number.
5. (Optional) Please upload a photograph of you at the Bargain Stone, if possible showing you shaking hands with someone through the hole.