Geology
See also: Geology of Shropshire and Longmyndian Supergroup
The geology dates back to Precambrian, and during the time would have been 60° south of the equator, the same latitude as the Falkland Islands. Shropshire would have been at the very edge of a large continent near the sea, which was being buckled by tectonic activity, causing volcanoes to form. The area had broad rivers; evidence of mudflats has been found. The rivers would have flowed out to sea, creating large estuaries; over time, the mudflats would have built up, and volcanic eruptions deposited ash in layers between the sand and mud. The primary rock of the Long Mynd is sandstone, usually coloured purple or grey. The volcanoes created the nearby Stretton Hills and the Wrekin, and eruptions would have been frequent. There are layers in the rocks of the Long Mynd that have preserved raindrop marks recording a passing rain shower. The raindrop marks were created when rain fell onto a layer of firm dry mud, and were then covered by another layer of mud, which filled them in and preserved them for 565 million years. Examples of these fossilised rain prints can be viewed today in the National Trust Tearoom Exhibition, in Carding Mill Valley. The layers of rock built up over the millennia to create an approximately 7,000 m (23,000 ft) thick layer composed of sand, mud, silt, and ash.
Towards the end of the Precambrian period, the volcanoes ceased their eruptions, and the rivers had dried up. Instead the forces that created the volcanoes caused the new rocks to lift and fold, creating mountains and valleys in the area. Much of the rock was melted during this period, underneath the Earth's crust, causing the mountains to continually change towards the latter part of the Precambrian. The Church Stretton Fault line was created during this period, and is still active today. The hill Caer Caradoc adjacent to the Long Mynd and from the same time is more volcanic in origin, and is thought to be the remnants of the great mountain chain.
During the Cambrian, Shropshire was flooded by the sea, after the Global Ice Age ended 545 million years ago. Thick layers of beach pebbles and white sand were built up against the sea cliffs that were once molten lava. During this time, the shallow sea played host to the huge explosion of new life which occurred during the Cambrian. Shropshire has some of the most historically important evidence in the explosion of life and in the naming and dividing of the Cambrian period. Trilobites that are found in the county are internationally important for deciding how the Cambrian is divided into smaller segments of time.
The Ordovician had Shropshire back to volcanic activity, and saw the county temporarily split in two, along the Pontesford - Linley fault line. Everything west of this line was ocean, while the east was dry land. The Iapetus Ocean was closing, bringing the two halves of Britain towards each other, and volcanic eruptions created the Cumbrian Mountains, and Snowdonia. Shropshire also saw volcanic activity. To the west of the Pontesford - Linley fault, volcanic rocks have been found. The other side of the fault line was quieter. The land was slowly eroded, and the sea gradually flooded it, so that only the tops of hills could be seen, such as the ancient Caer Caradoc. Towards the end of the Ordovician, the sea levels dropped, due to another ice age.
The Silurian period, occurring 439 million years ago, has been well preserved nearby, in Wenlock Edge. During this time, Shropshire would have been flooded again by shallow sea. Wenlock Edge would have formed during this time, and the fossils of ancient corals and shellfish can be found all along the Edge, preserved in limestone. Towards the end of the Silurian the Iapetus would have fully closed, and England and Scotland were joined. The closing of this ocean was important to geology in Great Britain. It caused most of our hills and mountains to align along the fault, northeast to the southwest.
During the Devonian, the newly formed Scottish Mountains had rivers flowing all over the land. Shropshire was no exception; these new rivers caused thick deposits in the area. Most of the rocks from this era are red sandstones, caused by iron in the rock. The area was known as the Old Red Sandstone Continent. These river sediments have traces of fossilised fish. Shropshire would have remained above water until the end of the Devonian, when the seas rose once again.
The Carboniferous was a time of great change for the area. Shropshire would have been near the equator, and the Old Red Sandstone continent had been eroded away; in the early part of the era, the county was under a shallow sea. However, tectonic activity pushed Britain out of the sea. South of Shropshire this effect was felt greatly, though Shropshire was relatively quiet. Mountains to the north were being worn down by rivers, creating enormous deltas that were colonised by plant life. A tropical forest took hold all over Shropshire, with ancient tree ferns and horsetails. Shropshire eventually crossed the equator during this era, and became a part of Pangaea during the Permian; the area would have been very similar to the Sahara Desert, and would have been in the vicinity, around 20° to 30° north of the equator.
The Triassic, Jurassic, Cretaceous and Tertiary were very quiet in Shropshire, and very little evidence can be found from these periods. The last Ice Age during the Quaternary has its effect on all of Shropshire, shaping the landscape as we see it today. The Long Mynd would have been under a thick Ice Sheet, several hundred metres thick. As the ice melted, it carved out the valleys and hills of the Long Mynd massif we see today. The small rivers, streams and brooks still very slowly carve out the valleys. The springs and bogs play a part in Church Stretton's economy, as the people bottle the mineral water that comes from the Long Mynd.
Today the steep and narrow valleys are covered in a thin layer of soil, with a low pH, able to support only strong grasses, rushes, and heathers. Beneath the soil the evidence of the ancient and chequered past can be seen, and the rocky outcrops and scree slopes are excellent places to view the different layers of ancient rock.
Since 2006, Cambridge University has monitored seismic activity in Long Mynd. The broadband seismometer is connected to the internet, and real-time traces can be viewed online here.
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