Geology of Shropshire

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Geological map of Shropshire.

Shropshire's Geology is very diverse and most rock types found in the British Isles can be found in the county too. There is also a large amount of mineral wealth, including lead, coal and iron in the county, which perhaps helped the area develop the first industry of the industrial revolution, in the Ironbridge Gorge area.

Upon looking at a geological map of the county, the most obvious feature straight away is the Church Stretton fault. This runs, initially, from South West Wales, entering the county of Shropshire in the south west, near the small town of Clun. It travels north eastwards through the county, dividing the county in two, before coming to an end near the town of Newport. The fault itself passes through Church Stretton, the location of the Long Mynd, and also passes close to The Wrekin. Another, smaller fault exists in Shropshire, the Pontesbury Linley fault, situated near the village of Pontesbury, south west of the county town of Shrewsbury.

The oldest rocks in Shropshire are to be found near Shrewsbury, on Haughmond Hill. The sedimentary rocks here are Precambrian in age, and quarried for use on roads. The hill itself provides an amazing view across large parts of mid Shropshire.

The Wrekin is a prominent hill near the town of Telford. The sedimentary rock types are varied around the area, but lava from various volcanic eruptions formed this landmark, however, The Wrekin itself is not a volcano, and never was. The primary igneous rock on the Wrekin is rhyolite which has a pinkish colour and is usually banded as it is a slow cooling viscous extrusive rock. A particularly good outcrop of rhyolite exists as you drive between Wellington and Shrewsbury on the new A5 by-pass. Intrusions of igneous rock have been quarried in the past at nearby Ercall Quarry. Here, the main type of igneous rock that can be found is Granophyre. At Ercall Quarry itself, you can see the boundary between Precambrian rocks and the Cambrian explosion of life.

Not far from The Wrekin is the famous Ironbridge Gorge, named after the bridge that stands over the River Severn near Madeley. The geological events that took place here thousands of years ago were what made the events that took place here in the Industrial Revolution possible, as the Gorge itself was carved out by an ice sheet, together with its melt water, towards the end of the last ice age, some 15,000 years ago.

Much of North Shropshire is a plain which is a basin of Permian and Triassic New Red Sandstone, overlain by Jurassic deposits in a small area near Wem. This basin continues north into Cheshire. Faulting has occurred within the sandstones, because of slippage during or after the filling of the basin. Escarpments form small prominent hills within the plain. The basin is bounded on the east by the Hodnet Fault, which runs roughly from Shrewsbury to Market Drayton. East of this fault the sandstone is thinner. In the north west of the county near Oswestry are outcrops of Carboniferous Limestone and the Coal Measures.

Igneous intrusions in South Shropshire, a sill of dolerite and a basalt intrusion, have formed the Clee Hills – Brown Clee Hill and Titterstone Clee Hill. These are two of the three highest points in Shropshire, and serve as outcrops for Old Red Sandstone, and also various coal measures and limestone. Brown Clee Hill is considered to be one of the best exposures of Old Red Sandstone that exists. South Shropshire was on the border of the Old Red Sandstone continent, explaining why it appears so prominently in the Clee area.

To the north west of Clee is Church Stretton, famous perhaps because it gives its name to the fault that runs through the town and the whole county. The Church Stretton hills were formed on a continental shelf, but buckled up into hills at the time of a continental collision, which formed the Variscan mountains. The most famous of these hills is probably the Long Mynd, which is Precambrian in age and forms the west side of the Stretton Valley. East of Church Stretton is Wenlock Edge, a Silurian limestone escarpment. The Wenlock Edge is the equivalent of the famous North American Niagara Escarpment, which comprises middle (Clinton Group) to Upper Silurian strata. These two escarpments were most likely in the same locale prior to the separation of the North American and European plates at the end of the Mesozoic Era, 60 million years ago. This is evident by the presence of the Mid-Atlantic Ridge. South West of Church Stretton, and at the westernmost border of England with Wales, is the very rural area of Clun. The rocks here are mainly Silurian in age, and whilst they are, on the whole, soft rocks that are easily eroded, the topography is very varied with an impressive landscape, and the hills were put to good use in Iron Age times with the use of fortresses on the hills around Clun and Anchor.