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The Stiperstones

The Stiperstones is an impressive ridge running NNE/SSW in the west of the county. Along the ridge are a number of dramatic exposures. These are made of a rock known as Stiperstones Quartzite. It is now an SSSI and NNR and is a popular beauty spot despite (or because of) it’s rumoured connections with the Devil (click here to see the reasons for notification).

It is an important landmark in Shropshire and has had a role in the industrial development of the area due to its geology – lead has been mined here since Roman times.  Click here to see the reasons for notification of the Snailbeach Mine as an SSSI.

Stipperstones

The Stiperstones Quartzite was probably deposited in shallow water with the conglomeratic bands possibly being laid down in a beach environment (alternatively it may be a deep water deposit with sediment accumulated by slumps due to fault movement and earthquakes nearby – this is being actively investigated by new research). The rock is very pure with a higher percentage of quartz than the similar, but older, Cambrian Wrekin Quartzite.

This cross-section of the area shows the quartzite that makes the ridge. The way it has been folded means the quartzite only breaks the surface in a few places.

One place the quartzite outcrops is at Nils Hill quarry near Pontesbury at the north end of the ridge. At quarries like this the structure and nature of the rock can often be seen clearly.

Nils Hill Quarry

All the tors of the Stiperstones ridge, such as The Devils Chair and Cranberry Rock show many of the same features, so here is a general description.

In many tors the steeply dipping beds of the quartzite can easily be made out.  There are also two sets of joints.  One set run at 90° to the bedding (these can just be made out in the photo) and the second set run 90° to the first set. 

The texture of the rock ranges from poorly sorted, coarse conglomerate, with sub-rounded quartz pebbles of up to 1 cm in diameter, to the main blocks of the tors which are fine grained. The conglomerate pieces may contain pebbles which are of other rock types that have been incorporated into the quartzite at the time of its formation. These include clasts of purple Longmyndian sandstone.

Along the ridge there are piles of boulder scree in which loose pieces of quartzite of all textures can be found. It is therefore unnecessary to hammer at any of the rock faces if visiting this site. Quartz veins can be found in many of the pieces some of which show well formed, if small, crystals.

The streams of boulders apparently flowing down the slope are ‘Stone Runs’, the result of solifluction. This is a process that was active during the last Ice Age when the groundwater was frozen and just the top few metres melted during the brief summer months. The resulting waterlogged ground slowly moved downhill, easily transporting blocks of rock fallen from the tors as it did so.

This Google Earth view of the stone runs is from imagery taken in 1999 and is looking NE at an angle of about 50 degrees across the central part of the main ridge. Click the image for a more detailed view

Google Earth view of the Stiperstones taken in 1999
The Stiperstones – GEOMORPHOLOGY

The Stiperstones is a ridge that has formed because of the relative resistance (hardness) of the Stiperstones quartzite compared to the other rocks surrounding it. The rocks to the west and east (Mytton Flags and Habberley Shales respectively) are much softer and therefore have been differentially eroded to form the slopes and low ground to either side of the ridge.

The ridge itself has been shaped most recently by the action of ice and frost shattering (freeze thaw) on the rock during the last ice age. This has created the tors that line the top of the ridge that make this site so recognizable from the surrounding countryside.

The Stiperstones – FOSSILS

The slopes to the west of the tors are made up of the rocks that were deposited on top of the quartzite. This sequence of rocks shows that the environments of deposition alternated from shallow water sediments with trilobites and shallow water brachiopods to a deeper water environment in which there are other trilobites and where graptolites were much more common.

The steeply dipping Mytton Flags are a good source of fossils. Beds such as these contain graptolites and trilobites.

The Stiperstones – INDUSTRY

On the slopes of the Stiperstones there was once a thriving mining industry.

This engine house (now demolished) and tips (now mostly landscaped) show some of the effects that this indusrty had at Snailbeach. Some remnants are still visible at the site now run by the Shropshire Mines Trust as a visitor attraction.

This mining industry was based around a series of veins that occur in some of the harder layers (mostly Mytton Flags) of rocks in this area. These veins are associated with the latest stage of igneous activity that occured in this area causing hydrothermal convection through the joints of the overlying strata. As the water running through these cracks cooled minerals carried in solution would have been deposited. Different minerals are deposited at different temperatures and this results in mineral zoning.

In the Stiperstones area the veins lie within two of these zones and relate to the three main minerals mined in the area. The lower zone contains lead and zinc whilst the upper (deposited at a lower temperature) contains barite. In general the lead and zinc were found in the central area of the mining district wheras the barite was found in the far west and to the east in Longmyndian rocks.

There were many mines in the area. However, only the Snailbeach Mine is accessible to visitors, by prior appointment and under guidance.

The lead was mainly found in the form of lead sulphide (PbS) known as galena. Galena is a distinctive metallic grey, cubic crystal and is the most common lead ore. It is not often found in well formed crystals but its cubic structure is usually fairly obvious.

Some of this lead ore also contained silver which the Romans, and later miners, extracted. Other minerals that can be found in these veins include, iron and copper pyrite, barium carbonate, lead carbonate, and zinc carbonate. There are places that can be (see map below) where it is possible to collect mineral specimens from the old spoil tips.

The ‘Rock Store’ at the Snailbeach Heritage Centre is a safe, designated area for mineral collection

Places which can be visited.

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