16 Jan. 2019
Presented by Prof. Brian Wilkinson to about 50 members and guests
Brian opened by noting that the Titterstone Clee & Clee were closely adjacent hills and had common features. At 533m above sea level Titterstone Clee is a distinctive local landmark. It is the third highest hill in Shropshire. He noted that it was the only hill in England shown on the 14C Mappa Mundi held in Hereford Cathedral. He did not know why this was but speculated that this may have been due to the wide range of minerals & rocks available from both Titterstone & Clee Hills: coal, ironstone, limestone, clays, building stone.
Brian considered that to understand the way in which these rocks had been exploited it was helpful to have a basic understanding of the geology. He described this briefly using a simplified geological cross section through the hills – shown below.
The hills form what geologists call an ‘outlier’ [an island of younger rocks of the Carboniferous period – 359 to 299 million years old] resting on older rocks [mostly red Devonian sandstones and marls – often referred to as Old Red Sandstone. The mineral resources are found in the Upper Carboniferous rocks. There are no rocks younger than the Carboniferous strata on either of the hills. The hills were not covered by the thick ice sheet during the last glaciation, which ended 12-13000 years ago, but the effects of frost action can be seen in the major screes lying towards the base of the hills.
There is archaeological evidence of Bronze Age burial cairns on both hills and a major Iron Age rock wall enclosure – 1.4 miles long- surrounding the top of Titterstone Clee. This is the largest Iron Age structure of its type in Shropshire.
The lowest Carboniferous stratum is the Oreton Limestone. Brian described how this had been extensively worked for building stone and as a source of lime. The lime was used on the fields and in mortar for building. There are numerous old lime kilns; the last one probably ended operating in the 1920s. The limestone was quarried where it outcropped on the surface, particularly at Oreton and Studley, but it was also extracted by tunnelling into the hillside near Studley.
Moving to a higher level up the hillsides there are a series of Carboniferous sandstones above which are the Coal Measures. Brian described how these were formed by the growth, then collapse, of large trees and other vegetation into swamps. These were then compressed by deposits of sand and clay sediments over them. These formed the sandstones and shales. This process was repeated a number of times over tens of thousands of years as the land surface rose and fell. Brian showed the record of a 1920 borehole drilled from the top of Clee Hill to a depth of about 450ft. At about 350ft coal was found. There were 4 to 5 principal coal seams ranging between 3 to 5 ft in thickness.
Around the periphery of the hills the coal could be reached by shallow workings called bell pits. These were used in the 13C and evidence of the shaft depressions and the surrounding circular spoil heaps can be seen in their hundreds to this day.
Deeper coal mining, which began in the 1700s, involved sinking substantial shafts on Clee Hill to about 500ft. The shafts had to penetrate about 200ft of hard igneous rock before reaching the coal-bearing strata. 40 shafts were sunk. The Barn Pit employed about 80 men. Mining conditions, working in candlelight and with water ingress, must have been terrible. Coal mining ceased in the 1920s and the shafts were capped in the 1940s.
The 1920s borehole log which Brian showed indicated iron-rich layers in the sandstones and ironstone nodules in the strata between the coal seams. As coal, limestone and fireclay were locally available for use in smelting a number of iron smelting hearths were established around the Clee hills.
Dhustone [Olivine Dolorite]
At the top of Titterstone Clee & Clee Hill there is a hard, igneous, rock known locally as Dhustone. Brian described how this was formed by molten lava from depth forcing its way to the surface and splitting the Carboniferous coal measures open to form a horizontal 60m layer of rock on cooling. Geologists call this type of structure a ‘sill’. It is characterised by strong vertical joints formed as the lava shrinks as it cools.
Commercial quarrying of this hard rock began in the 18C. It was widely distributed as a building stone [e.g. Cardiff docks], stone sets and aggregates. The stone from Titterstone Clee was transported by wagons down an impressive incline to the village of Bitterley, from where a rail link carried the stone to Ludlow. From the car park at the top of Titterstone Clee many of the old quarries can be seen, together with the remains of the old concrete crushing and grading structures. It is also possible to walk down the old wagon incline, now grassed over.
In the early 20C quarrying activity moved on to Clee Hill. From here [e.g. Magpie Quarry] the stone was transported by overhead cableway to a railhead near Cleobury Mortimer.
In the 1860s 2000 men worked in the quarries and in 1910 400 000 tons of rock were extracted.
The Dhustone is still quarried. There is a good observation point with information boards on Clee Hill. This can be reached from a path leading to the east from the Titterstone Clee access road.
The chair, Jonathan Hopkinson thanked Prof. Wilkinson for his talk which was enhanced by many images. This was followed by a lively discussion. The audience’s attention was drawn to Benson’s Brook which flows off Titterstone Clee towards Bitterley. There is a reservoir on the brook which was a source of water for a hydro-electric station [now disused] near Bitterley. Being built in 1885 this must be one of the earliest hydro-electric schemes in the UK.
Brian gave a number of information sources on Titterstone Clee and Clee Hill, in particular he noted:
Jenkinson. 1983 Titterstone Clee Hills
Wilkinson, G. Wilkinson. and Rosenbaum,M.S. 2005 A Walk on Titterstone Clee and Clee Hill
Cleobury Mortimer Footpath Association Web site