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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.


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.


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. 

 

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