The limestone wall here is another example of a limestone construction. It now forms part of a sheep enclosure but was once a section of walling that surrounded the yard of Lalu Barn. The barn was demolished in the late 1960s.
Lalu Barn Borehole
In the summer of 1967, the Institute of Geological Sciences drilled a borehole near Lalu Barn to prove the sequence of rocks under Bredon Hill.
Samples were taken as round lengths of rock core that were measured and logged by geologists who described the rock type, colour, fossils and its physical condition, for example if it was fractured.
The Institute of Geological Sciences is now known as the British Geological Survey. It is the national (UK) organisation for the collection and interpretation of geological data.
Sequence of Strata
The borehole was drilled to a total depth of 195m and proved from top to bottom, rocks from the Inferior Oolite (36m thick), Upper Lias ( 110.5m), Middle Lias (41.2m), Lower Lias (7.3m).
The Inferior Oolite limestone that forms the top of Bredon Hill was found to be generally heavily fractured and contained many solution cavities.
The remainder of the borehole at depth was from the Lias, a term that groups together the lower or oldest parts of the Jurassic. The Lias is mostly mudstone, sometimes containing harder bands of sandstone and limestone. The mudstone generally weathers to become soft clay.
The diagram below shows this sequence imposed on a relief model of Bredon Hill. The names of the rocks in this diagram are those currently used by the British Geological Survey, with the original names in brackets.
Lias clay and marlstone
The Upper Lias is predominantly mudstone that was deposited in a deep-sea environment. Fossils included ammonites and fish remains.
The Middle Lias consists of a sequence of sandstones, silts and thin limestone that suggest the sea environment was shallow at the time the Middle Lias was deposited. At the top of the Middle Lias there is a very hard band of rock 6m thick known as the Marlstone Rock Formation.
The picture above shows what this area looked like during the time when the Middle Lias rocks were forming.
The Lower Lias is much thicker than proved by the borehole and consists of a thick sequences of mudstone, deposited in a deep-sea environment.
The clays were once used for making bricks. There was a brick works at Upper Comberton, on the north side of Bredon Hill, and at Strensham to the west, where fossils of the marine reptile, the Ichthyosaur (large creature on the right in the image), were discovered.
The picture above shows what this are looked like when the Lower Lias was forming.
Whilst Bredon Hill limestone was used for the construction in the villages on the south side of the hill, it has been noted that timber frame buildings on a limestone platform are more common on the north side of the hill. Sometimes brick was also used, as in the arches of the stables at Sundial Barn.
The small brickworks at Upper Comberton would have supplied handmade bricks for infill in the timber frames. In the 19th century when a railway system existed, machine manufactured brick could be brought into the area from further away.
The Lower Lias mudstones are perfect for brick making as they weather into malleable clay that can be moulded and fired in furnaces to make a relatively hard-wearing building material.
In 1839, the bones of an Ichthyosaur were discovered in the brickworks at Strensham, near the M5 motorway service station. The Ichthyosaur was a large marine reptile that was very common in the Liassic Sea. Its sharp teeth indicate that it was a predator perhaps living on a diet of fish and ammonites.
Their remains have generally been discovered wherever the Lias outcrops. Complete skeletons can be discovered at either end of the Liassic outcrop where it is exposed in cliffs, at the local museums at Whitby, North Yorkshire and Lyme Regis, Dorset, for example.
Task 6 Question
Why are clays used for brick making?
Is it because
a) They can be easily moulded into shape
b) The bricks are waterproof
c) They can be easily dug out of the ground
d) Clay comes in a range of colours