Light & Dark Shap Granite kerbstones. Leeds
Time on my hands
Dark Shap Granite. Albert Road, Middlesbrough.
A recent visit to family in Cornwall gave me the opportunity to have a look around this beautiful far corner of England.
This tale begins approximately five hundred million years ago when the north of Scotland was attached to a continent called Laurentia. The rest of Britain was joined to a continent called Eastern Avalonia. Scandanavia was part of a continent called Baltica.
Tectonic forces caused these three continents to move towards each other, the collision resulted in the loss of a huge ocean, the Lapetus, and the creation of a mountain range, on the scale of the Himalayas. This event, during which the north of Scotland became joined the rest of Britain, was called the Caledonian Orogeny and lasted about one hundred million years.
Orogenesis – The birth of mountains.
The mountain range that was formed during the Caledonian Orogeny has long since been eroded away but the rocks that were formed during this period remain, one of which is Cumbrian Shap Granite.
Shap granite is described by geologists as a coarse grained granite, formed by the cooling of a large body of igneous rock, called a pluton, which was intruded into the pre-existing Cumbrian rocks. Shap granite is very distinctive and easily identified by the large crystals (phenocrysts) of pink orthoclase feldspar contained within its matrix.
The granite intrusion is limited to an eight square kilometres area on the Fells, a couple of miles to the south of the village of Shap.
There are two rocks called Shap granite, pink granite and blue granite. Pink granite is a true granite, it is an igneous rock which originates from a large reservoir or Batholith, deep within the earth’s crust. Blue granite is a metamorphic rock known as Hornfels. The Hornfels was formed when the native rock around the granite intrusion was altered by temperature and pressure. The zone of altered rock around the intrusion is known as a Metamorphic Aureole.
Both the pink and blue granites are exploited for commercial purposes. Pink granite when cut and polished is used as an attractive and extremely durable building stone. With the coming of the railways it became a popular architectural stone with the Victorians and has, and still is, been used as a decorative stone on buildings throughout Britain. Blue granite is usually crushed and used as aggregate for concrete or as hard-wearing road chippings.
Five to six thousand years ago, the first farmers arrived in Eastern Cumbria. The main rock type on the low moors and valleys around the Shap area is Carboniferous Limestone. The land around Shap is fertile and well drained, an ideal place for the pastoralists and their animals to settle. Once communities became established they marked the land with their stone and earth ceremonial monuments.
The valleys and moors around Shap are littered with pink granite boulders, this was not lost on our ancestors and the majority of the stone monuments in the local area are built almost entirely of Shap granite boulders. The most obvious reason for this is availability but I believe that our ancestors may have placed a spiritual value on the distinctive granite boulders. The large feldspar crystals in the granite are the colour of flesh, The texture and colour of weathered limestone can resemble bone.
A few stone circles they have a single limestone boulder or in the case of the Oddendale Concentric circle, two stones, one in the outer ring and another between the two rings. Some, but not all, of the of the regions monuments are intervisible, forming a long chain of ritual monuments along the Lowther and Eden valleys.
Large single erratics are known as Thunder Stones; No one knows the origin of the name other than a general belief that these stones were cast down to earth by the gods or a race of giants.
Eastern Cumbria is particularly rich in prehistoric monuments; the village of Shap was once the location of one of the most impressive monuments in Northern mainland Britain, the Shap Avenues. Little remains of this monument but by looking at the archaeological remains and antiquarian accounts we can build up a picture of what it looked like. A few years ago a good friend and I researched the Shap monuments, an account of our research and fieldwork can be found here Shap MA Blog
The reasons why Shap and the North of Britain are littered with granite boulders probably alluded our ancestors. Up until the beginning of the nineteenth century, the occurrence of these stones was used as evidence of a catastrophic flood event as described in the bible. This theory, diluvianism, remained unchallenged until 1840 when a young Swiss naturalist called Louis Agassiz brought a new theory to Britain based upon his observations on the movements of Glaciers in the Alpine regions.
Agassiz toured Northern England with the Reverend William Buckland, Professor of Geology at Oxford University. Their theory of glaciation and the glacial transportation of material was not readily accepted by the scientific establishment of the day but further evidence-based studies gradually gained support and glacial theory was accepted.
These ice transported boulders became know as glacial erratics, to further the study of glaciation during the nineteenth century local naturalist groups were enlisted throughout the North of England and Scotland to help. These groups often formed Boulder committees who engaged in fieldwork, logging locations and rock types of erratics throughout the Northern Britain. This information along with the study of landforms was then be used to build maps tracking the movements of the ancient ice sheets and glaciers.
Many Shap granite boulders have been found in the Tees Valley, some have even been given names, the Bulmer Stone in Darlington and the Great Stone in Deepdale. Others have been used as curiosities on village greens and parks. There is even an account of a group of boulders beneath the sea, close to the mouth of the River Tees.
Erratics apart, Teesside has another link with the Shap area. Behind the village is a large Limestone quarry; attached to the quarry is an industrial site that processes the limestone. The site was formerly owned by British Steel and is currently operated by Tata Steel. Limestone is an essential ingredient in the production of iron and steel, it acts as a flux, removing impurities from the molten iron and helping slag to form. The basic recipe to create one ton of iron is; two tons of iron ore plus one ton of coke plus half a ton of limestone.
The recent decline in the iron and steel industry in Scotland and the North of England has led to a collapse in the market for flux-grade limestone and the closure of many quarries. The Hardendale quarry is now closed and the limestone plant at Shap is currently up for sale.
The Shap area is a place that continues to draw me back. The terrain is soft, the landscape is dense in history, the vistas are open and the skies can be endless. My genius loci exists amongst the stone circles and limestone pavements on the rolling uplands of Shap.