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Geology
- The Geology of Castlemorton Common
- It all started 677 Million Years Ago
- 566 Million Years Ago
- The next 200 Million Years
- 300 Million Years Ago
- 248 Million Years Ago
- 2 Million Years Ago
- 26000 Years Ago
- 10,000 Years Ago
- Road Stone and Building Stone
- Conclusion
- Safety
The Geology of Castlemorton Common
The defining geological feature of the common which has impacted most on the use of this land as a common, is the poor thin soil which has developed on top of the “Malvern Gravels”. The gravels were washed off the hills between 1.8 million years ago and 10,000 years ago (this is recent in geological time!). In order to understand more about the geology of the commons it is first necessary to go back hundreds of millions of years in time and discuss the rocks of the Malvern Hills which are among the oldest in England.
The rocks underlying the Castlemorton Common area tell the story of a journey which started near the South Pole, hundreds of millions of years ago. Over hundreds of millions of years this area has moved to its present position as tectonic plates of the Earth’s crust have been affected by earth movements and mountain building. The speed of movement is about 2.5 centimetres a year (the same rate that finger nails grow!).
It all started 677 Million Years Ago
Deep in the Earth’s crust, magma trapped underground, cooled very slowly and crystals grew until they were large enough to be seen easily by the human eye. After the rock solidified, more magma rose up through cracks and solidified to form pink veins similar to granite in composition. Earth movements put the rock under massive temperature and pressure stress. The rock was pushed up along a line of weakness in the Earth’s crust and was eventually uncovered by erosion (Fig 1). These rocks are known as the Malverns Complex, and can be seen in the Gullet quarry.
566 Million Years Ago
At this time there was a collision between a continental and an oceanic plate. The heavier oceanic crust was forced down under the lighter continental crust until it became hot and melted. Molten magma rose again but this time it reached the surface as volcanoes. Some of the volcanoes erupted under the sea. The lava cooled quickly in contact with the cool sea water forming a solidified crust round globules of molten lava, pillow lava. Further lava erupted and a pile of pillow lava built up on the sea floor. Layers of ash were thrown out by explosive eruptions. These volcanic rocks, are known as the Warren House Formation
An outcrop of the Warren House Formation can be seen on the footpath on the east side of Hangman’s Hill between the Pink Cottage and Dales Hall (SO 7652 3895). The stone has weathered to pale pinks, blues and greens. The crystals in volcanic rock are small because they cooled quickly.
The next 200 Million Years
Over the next 200 million years, this area was under the sea with only occasional distant volcanic eruptions and one period of glaciation. Between 417 and 443million years ago, when this area was south of the equator, there were clear tropical seas which lapped against a shoreline in the Malvern Hills area. On the sea floor layers of shell fragments and layers of sand were deposited and formed limestone and sandstone rocks. These rocks are found in the ridges to the west of the hillsSwinyard and Hangman's Hill. Fragments of these layered sedimentary rocks can be found in the streams crossing the commons to the east of the hills below Swinyard Hill between Foxhill and The Poplars.
300 Million Years Ago
This area of the country continued to move slowly 
northward and around 300 million years ago two major continents of the earth collided. This happened at about the same speed that the continents are colliding today (millimetres a year the same rate as finger nails!). The collision crumpled the landscape creating mountain ranges. The ancient rocks of the Malverns Complex where pushed up and the rocks to the west of the hills were folded. British Camp, (the Herefordshire Beacon), was thrust to the west out of line with the more northerly Malvern Hills ). Further movement of continental plates changed the pressures around Malvern Area. A fracture in the Earth’s crust developed along the east side of the Malvern Hills. The plates started to move apart in a series of movements, which dropped the Worcestershire basin down 2000 metres and developed a rift valley where the Severn Valley is today.
Sometime later further geological instability thrust Herefordshire Beacon (British Camp) to the west and out of line with the rest of the Malvern Hills.
Reproduced from Ordnance survey information with the permission of The Controller of her Majesty's Stationary Office, Crow Copyright, Malvern Hills Conservators, Licence number 100031850
248 Million Years Ago
About this time the world was also going through a mass extinction in which 75-90% of species became extinct. The Malvern area was an arid region in a huge continent. Fine-grained sediment was blown into the basin or deposited by meandering seasonal streams and in shallow lakes. These sediments formed the red Mercia Mudstones that can be found in the banks of streams on the common such as those of the stream below the Millpond (Extreme caution should be used if visiting this site because it is steep and very slippery).
About 220 million years ago the arid conditions are interrupted briefly by a humid period when the grey beds of Arden Sandstone Formation formed in a brackish environment. Ridges of the Arden sandstone are found south of the Millpond and Coombe Green.
About 200 million years ago the seas covered the land again and formed the marine limestones seen further east in the Cotswolds. These limestones have all been eroded from the area of the Malvern Hills. Later there was a further collision of continental plates which formed the Alps 65 million years ago.
1.8 Million - 10,000 Years Ago
The climate fluctuated between warm interglacial, and freezing glacial conditions during the Ice Age. During the glacial periods summer temperatures reached between -6 and -12 Centigrade and in the winter down to -20 Centigrade. The land was covered by ice sheets with only the peaks of the Malvern Hills sticking out. The grinding ice scoured the lowlands. The extremes of temperature fractured the exposed rock. Water in cracks expanded as it froze shattering the rock and produced angular rock fragments. In warmer periods the ice retreated leaving the gravel deposits behind and these were washed down on to the Castlemorton Common area.
When the ice melted its weight on the land was removed and the land suffered a rebound (it sprang back up). With the land rising relative to sea level the streams crossing the commons were rejuvenated and could cut down into the underlying rock. On the commons there are deep steep sided valleys, such as the valley to the north of Hollybed Common. This valley starts very abruptly as does the valley on Hollybush Common. The steep sided valley, just to the north of All Saints Church at Hollybush, is the head of a small stream, which has cut a deeply incised valley through the Arden Sandstone into the underlying mudstones. The harder sandstone supports steeper slopes in the area than the softer mudstones. Along the valley is a string of cottages and cultivated land. On the higher ground is common land. The Arden Sandstone is permeable and the underlying mudstone is impervious to water. There is a spring line at the junction between the two. Near the head of the small valley is a landslip area, the surface of the mudstone has been lubricated and rock above this level has slipped on the steep valley side.
The stream on Castlemorton Common shows a couple of stages of rejuvenation, with river terraces marking the former levels of the valley floor (Fig 6). Here is evidence that the valley was cut by a far greater volume of water than that flowing today. The scars of old meanders on the valley sides have greater amplitude than the meanders of the present day stream.
26000 Years Ago
Between 26,000 and 10,000 years ago the River Severn, which used to flow north into the Irish Sea, was diverted by glacial advances to flowing south and its present day course, cutting the Iron Bridge Gorge in the process. As it flowed through the Worcestershire basin terraces of gravels were deposited along the edge of the river’s flood plain which was up to three times as wide as today. Remnants of the highest (main) Terrace can be found on Hollybed Common and Castlemorton Common. 
The second (Worcestershire) terrace is found over a large part of the common. At Ripple near the M50 the terrace is up to 3m above the flood plain. Water rounded pebbles can sometimes be found alongside angular stones in the soil of the common where the Malvern Gravels have mixed with the river terrace deposits.
10,000 Years Ago
The climate became much the same as the modern day climate. However that may soon no longer be accurate with the onward march of climate change. The changes in the geology of the area for the last 10,000 years have largely been due to man’s actions.
The Human-Geology Interaction
Road Stone and Building Stone
Large quarries at Hollybush and The Gullet were worked for roadstone. The Malverns Complex stone was particularly good for road stone because it is very hard and breaks into irregular angular shapes which make them good for the road bedding (look out for any roads in the are made of pinkish stone these are made of Malvern Complex). In 1900s concerns were being raised about the extent of quarrying on the Malverns and in 1924 a new Malvern Hills Act gave the Malvern Hills Conservators enough power for compulsory purchase land for the following five years. Finances were restrictive and in most cases they were forced to buy the land around the quarry to prevent the quarry companies expanding rather than purchasing the site itself. 
Quarrying for road stone finally stopped in 1970 due of the changing economics of the industry and the old quarry licences coming to an end. The Malvern Hills Conservators eventually bought the quarries and the most recent, Tank Quarry in North Malvern, came into their ownership in 2007. On the east side of Swinyard Hill are two disused quarries, Swinyard and Castlemorton Quarries.
There are the remains of a small quarry on the hillside above Dales Hall, where Precambrian volcanic rocks were quarried.
Along the ridges of Arden Sandstone between the Mill Pond and Coombe Green areas there are the remains of many small pits some of which date back to mediaeval times.
Arden Sandstone is recorded as being used in the ramparts of the hill fort at Midsummer Hill so there may have been quarrying of this rock as far back as the Iron Age. The sandstone quarried here was used as a building stone despite being soft and easily weathered because it is formed in layers and is easy to cut, unlike the 
Malverns Complex rock which cannot be easily cut and shaped.
There used also to be pits in the mudstones, where marl, a red clay rich in lime, was extracted for use on the fields. These are now overgrown and no longer visible.
Conclusion
The Castlemorton Common area gives a good example of how millions of years of geological time have influenced the way man has used the area for the last few thousand years.
The low nutrients content of the top soil, a result of its parent rocks, has meant cultivation of the land was not worth the effort when better land was available. The area proved more useful as a mineral resource which has resulted in quarries ranging from, the many small hollows around the common, right up to the huge extractions at the Gullet. The early quarrying made the site even less desirable for agricultural improvement later on, due to the difficulties of cultivation of such uneven ground. The large quarries do however have the lasting advantage of allowing us to see the geology clearly.
The poor soil effectively made the land the “Waste” land for the Land Lords of the middle ages. It was left uncultivated and local people were given rights in common to use the resources of the area hence, common land. The use of the land as unimproved common land, in particular for grazing, has meant the geological features of the area have not been lost under the plough. Some of the flatter areas were ploughed for potatoes as part of the War effort but have now been returned to Common. Today the common has various layers of protection. The north half of the common is a Site of Special Scientific Interest, a designation given by Natural England that provides a nationally recognised protection for a site due to the significant wildlife present. The land owned by the Malvern Hills Conservators is protected under the first of the Malvern Hills Acts which stated they must “preserve the natural aspect of the Malvern Hills and commons and protect the trees, bushes and turf from spoilation”. In addition the whole common is protected by the fact that it is common land where nothing should be done to impinge on commoners’ rights.
The rich variety of the geology has meant this area is part of the Abberley and Malvern Hills Geopark. One of the partners in that Geopark is the Herefordshire and Worcestershire Earth Heritage Trust who were commissioned by the Malvern Hills AONB to do a study on the geology of Castlemorton Common, a Local Geodiversity Action Plan (LGAP). If you would like further information on the geology of Castlemorton Common, the report (LGAP) is available from the 4Cs website.
Safety
Please use caution if you visit any sites mentioned. Many sites are muddy and slippery and when entering quarries you should be aware of the risk of lose and falling stone. Do not climb in any quarries.
