Home > Start > Contents > A Tour of the Stone Slate Regions > Ordovician
  • Introduction: Stone-slate geology
  • Stratigraphy
  • Rocks and climate
  • Map
  • Cretaceous - Wealden
  • Jurassic
  • Permian and Triassic
  • Carboniferous
  • Devonian - Old Red Sandstone
  • Silurian - Pridoli: The Tilestones
  • Ordovician
  • In the region south of Shrewsbury stone roofs have been made with rocks of Ordovician, Silurian and Devonian age. Around Church Stretton it is possible to cross all three periods in the space of 10 miles. This makes for interesting roofscapes and difficult research. The rocks that have been used from the Ordovician range from examples which are typical of many other sandstones (except perhaps in colour) via the daunting and variable Harnage Slates, to the unusual dolerite of Corndon Hill. Nowadays they are often found mixed together on buildings or even on individual slopes. 
    The Ordovician in Shropshire lies along a narrow strip running north-east to south-west from Harnage to Aston on Clun. The roofing stones have come from the Cheney Longville Flags, the Chatwall Flags and the Hoar Edge Grit; all in the Caradoc.
    Silurian . .
    . Ashgill  .
    Ordovician Caradoc  Onny Shales 
    Acton Scott Group 
    Cheney Longville Flags 
    Chatwall Sandstone 
    alternata Limestone 
    Chatwall Flags 
    Harnage Shales 
    Hoar Edge Grit 
    . Llandeilo .
    . Llanvirn  .
    . Arenig .
    . Tremadoc .
    Cambrian . .
    The stone slates from the area around Acton Burnell and Pitchford exemplify why stone roofs are so attractive and interesting. They are variable, highly textured and some are so contorted and so hard to make into a roof that they would only ever have been used when the difficulties of transport over even short distances inhibited the use of easier slates from as little as 10 miles away.
    There are two beds. One, a fine grained sandstone, shown here, has a coarse texture; the other which is shelly is even coarser and splits along the fossil shells of a brachiopod (like a cockle) called Orthis subquadrata. They were quarried together and mixed on the roofs producing what are probably the most uneven and highly textured roofs in Britain. Only a few buildings now remain with Harnage (a contraction of Hoar Edge) slate roofs but they are all important. Until recently these roofs were proving impossible to conserve and in desperation substitute stone slates from all over the country had been used. Happily after research and a lot of effort by English Heritage a very small quarry was opened temporarily to look after these few buildings. Since then, St Michael and All Angel's church at Pitchford has been re-roofed and enough stone has been made to complete the re-roofing of Pitchford Hall. 
    The hill to the west of Cheney Longville has been extensively quarried and some, or at least one, has produced roofing for local use. It is not known over how big an area these stone slates were used. Certainly there are very few in the immediate vicinity of Cheney Longville but there are many roofs of similar stone within a ten mile radius. It will take some detailed geological research to determine where they all originated. 
    The Chatwall Flags (also known as Soudley Sandstone) are reputed to have been used for roofing but it was actually obtained from the alternata limestone which overlies the Chatwell Flags in shallow pits in the fields above the present quarry. The beds are packed with with the flat fossil shells of another brachiopod, Heterorthis alternata, which gives it its fissile quality. There are still a few alternata roofs in the Hope Bowdler/Church Stretton area.
    In earlier versions of this page the Cordon Hill roofing was described as 'an igneous intrusion of dolerite which splits into thin plates as a result of close-set jointing'.  This is incorrect. It is a very fine, laminated siliceous sandstone. In Vernacular Buildings of Shropshire (Moran M, 2003 Logaston Press, Almeley, Herefordshire, p42 ) it is described thus: 'The hill itself is a large dolorite intrusion ... however on the south western slope of the hill the altered Hope Shales on the margin of the dolorite produce finely laminated material which was extensively quarried for roofing and flooring.' 

    It was used for roofing in the 15th century at Llandrinis a few miles away but has also been found on roofs in Shrewsbury.

    'Slates' on Cordon Hill
    In a region with so many different stone slates it is difficult to give an overview of the roofs. A typical roof from the district around the two flagstones would be simple on plan with few intersections. Where valleys exist they are lead lined today. Overall the appearance is reasonably flat which contrasts strongly with the highly textured, uneven Harnage roofs.
    Roof in ClunHarnage slates on Langley Chapel