Geology

Rea Valley, with-Bromlow Callow in the distance

It is a truism that landscape reflects the rocks beneath the surface, but in the case of the Stiperstones-Corndon area there are a number of very specific links which have a most distinctive effect on the resulting landscape character. The landscape area in question corresponds closely with the Shelve Ordovician Inlier. This is a distinctive suite of rocks with a roughly semi-circular outcrop. Its base-line is the geological fault running NNE-SSW down the western flank of the Long Mynd from Pontesford to Linley. Between these points it spreads westwards in an arc as far as the Marton valley, embracing the Stiperstones ridge on its eastern side, the parallel outcrops of the lead ore bearing Mytton Flags giving the lead mining settlements from the Bog to Snailbeach on the west flank of the Stiperstones and from White Grit through Roman Gravels towards Minsterley. Between these two mining areas, through the village of Shelve, and again west of Roman Gravels from Corndon, through Stapeley Hill and Hope the rock sequence contains several beds of volcanic rock and intrusions of igneous (originally molten) rock which give shape to the distinctive curved plateau of Corndon and were themselves of economic importance for quarrying as road metal and building stones.

The landscape and socio-economic effects of this suite of Ordovician (490-450 million year old) rocks can be clearly considered in at least three different areas. Most familiar is the Stiperstones ridge itself – the magnificent line of glistening white quartzite crags centred on the highest point of Manstone Rock with the Devils Chair to the north and Cranberry Rock to the south. These crags or tors were formed during the last Ice Age by freezing and thawing of the hard quartz rich rock. The resultant scree that has fallen off them is slow to produce a very acid soil with a most distinctive flora; whilst the freeze/thaw action distributed the scree into polygons on the flatter ground but stripes down the slope, giving an excellent residual tundra landscape.

The presence of economically important minerals – lead, zinc and barytes – in the succeeding Mytton Flags westwards has resulted in a most distinctive landscape of mining, both in terms of its history and settlement pattern. The mineral rich ores are concentrated in veins running roughly WNW-ESE, i.e. at right angles to the main strike (trend) of the rocks. Thus there is a characteristic pattern of discrete settlement on each of the major veins at the Bog, Pennerley, Tankerville, Perkins Beach and Snailbeach, then again at White Grit and Roman Gravels further west. These provide centres of geological, social and economic interest to both the local communities and to visitors. The history of lead mining goes back to Roman times as evidenced by the discovery of a pig of lead with the stamp of Emperor Hadrian near Linley. There are ‘tile stones’ on the southern flank of Corndon; unique, metamorphosed, water-lain, volcanic tuffs. These were used for roofing tiles of which at least two roofs remain.

But geology influenced activity in the area right back to prehistoric times, with an important stone axe factory in the igneous rocks at Hyssington exporting its products along recognised routes across the hills, such as the Clun-Clee Ridgeway in early Bronze Age times. The high points of the hills were also of cultural importance with burial chambers on the summit of Corndon and a stone circle on the ridge of Stapeley Hill. The local use of stone in its varying types can be traced right across the area giving distinctive local character to villages and hamlets. Most distinctive is the Stiperstones Quartzite itself, though not very popular to  local masons because of its hardness. Further west some of the volcanic rocks have been used extensively – the hard, grey Weston and Hagley volcanics around Priest Weston, the Whittery volcanic rocks used extensively in Chirbury and surrounding villages, and around the edge of the Shelve Inlier the overlying younger rocks including Coal Measures sandstones at Westbury and Pontesbury, or the very distinctive Pentamerus Sandstone in the south at Norbury and Wentnor.

There are equally a number of points of purely geological interest that are of sufficient clarity to help interpret the region to the general visitor. Apart from the Stiperstones ridge and the mining areas mentioned above there are exposures of rock in old quarries and roadsides which add further interest and explanation. Notable amongst these are sites up the main Bishop’s Castle to Shrewsbury road running through the centre of the area. In particular these are from south to north: Tasker Quarry where the previously visible volcanic and sedimentary rock sequence is becoming very overgrown; Hope Road junction where the folded rocks of the Ordovician are spectacularly shown in a cliff behind the bus-shelter; and thirdly the Hope Mill Quarry, currently part of the Hope Valley Woodlands nature reserve of the Shropshire Wildlife Trust. The last has several points of interest including the unconformity (contact point) between the Ordovician and overlying Silurian rocks and the Silurian rocks of the quarry used for local building stone. There are plenty of ice-margin features and one very scarce ‘plunge-pool’ location where huge floods resulted in deep pits. Similar features are more common in Iceland.

Geological site access and interpretation are scarce across the area, despite this underlying importance to the natural and cultural heritage.