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A TOUR OF THE STONE SLATE REGIONS
  • 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
    		•
    Rocks of Carboniferous age extend from the Bristol area, through South Wales to Northumberland and reappear in the Glasgow - Edinburgh belt of Scotland. They are divided into two main subsystems: the older Dinantian or Carboniferous Limestone, and the Silesian, which contains the Namurian or Millstone Grit and the Westphalian or Coal Measures. The majority of Carboniferous sources of roofing stone in England are Silesian sandstones which are most important in Yorkshire, Lancashire, County Durham, Northumberland and Cumbria, but they have also produced locally important stone slates in Bristol, South Wales and in the Welsh Marches. 
    GEOLOGY
    The rocks of the Upper Carboniferous (Silesian) are classified into two series: the Namurian or Millstone Grit and the Westphalian or Coal Measures
    Permian .
    Carboniferous
    Silesian Upper Westphalian including Pennant Measures
    Lower Westphalian / Productive Coal Measures
    Namurian / Millstone Grit Series
    Dinantian Carboniferous Limestone
    Basal Conglomerate
     
    Devonian .
    Within the Carboniferous there are a lot of named rocks and many of these have produced stone slates. The table for the South Pennines gives an idea of how complex the situation is. (Table after Ian Thomas in Roofing Stones in the South Pennines)
    Named rocks used for stone slates in the South Pennines 
    Lower Westphalian / Coal Measures. 
    Marine marker band    		 .
    Gastrioceras listeri Wingfield Flags, Silkstone Rock, Penistone Flags, Grenoside Sst, Greenmoor Rock, Brincliffe Edge Rock, Loxley Edge Rock, Upper Band Rock, Milnrow Sandstone 
    Gastrioceras subcrenatum Crawshaw Sst, Woodhead Hill Rock, Sandstones below the Red Ash Coal, Sandstones above the Yard Coal
    Namurian / Millstone Grit. 
    Stage    		 .
    Yeadonian  Rough Rock, Rough Rock Flags,
    Marsdenian

     

    		 Huddersfield White Rock, Beacon Hill Flags, Pule Hill Grit, Heyden Rock, Rivelin Grit, Chatsworth Grit, Readycon Dean Series, Redmires Flags, Roaches Grit, Corbar Grit, Ashover Grit, Five Clouds Sandstone, Brown Edge Flags, Rushtonhall Grit, Walker Barn Grit.
    Kinderscoutian Kinderscout Grit, Shale Grit, Edale Shales
    Alportian Edale Shales
    Chokierian Edale Shales
    Arnsbergian Edale Shales
    Pendelian Edale Shales
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  • BRISTOL, FOREST OF DEAN AND SOUTH WALES
    • Pennant roof at St Fagans Welsh Folk Life Museum Close up of Pennant slates
    The Pennant Measures are in the Upper Westphalian. There is a long history behind their use in this region. Archaeological studies on many Roman villas have turned up diamond pattern Pennants. Most Pennant roofs disappeared long ago although some have been saved at St Fagans Welsh Folk Museum. The quarries were in the Clivedon area near Bristol, the Forest of Dean and throughout the coalfields of South Wales.
    THE SOUTH PENNINES
    In the north of England the Carboniferous rocks occur in mountainous areas so that many rock horizons can outcrop within a small distance. Consequently the geographical distribution of the stone slate types is very complicated and several different looking slates can occur within a region. This aspect of the conservation of stone roofs was investigated for the report on the Grey Slates of the South Pennines. The properties used to define specific slate types are described in The Appearance of Stone Slates page. In the South Pennines seven types were proposed to reasonably cover the variety of colours, textures and sizes. Attempts are now being made to establish production of each type either continuously for those with a big market or intermittently for types which have only a few roofs.
    Historically there were hundreds of quarries in the region producing roofing, walling, flagging etc. Almost one for every village. Whilst they would all have originally been small serving a local community eventually some of those closest to the industrial and commercial regions of Cheshire, Lancashire and Yorkshire became very large. Cracken Edge near Chapel-en-le-Frith, Glossop Low and Harden Clough near Holmfirth stand out. The latter had such a good reputation that it was known as the Magnum Bonum.
    NORTHERN ENGLAND
    North of the Peak Park the Carboniferous runs up the centre of England and passes off-shore in Northumberland. Throughout the area it has produced stone slates from a variety of rocks but its greatest exploitation has been around the industrial towns. There are literally hundreds of quarries - too many to list, but there were some important centres of production in West Yorkshire and East Lancashire.
    The Elland Flags (equivalent to the Wingfield Flags of Derbyshire) were worked to the east of Halifax at Northowram, Hipperholme, Southowram, Elland and Rastrick and several quarries are still operating in the area. The same rock is known as the Rochdale Flags at Upholland, another important quarrying area. To the West at Halifax and Huddersfield the Rough Rock Flags have been exploited to a limited extent and elsewhere in Lancashire and Yorkshire the Moorside Flags, Beacon Hill Flags and Readycon Dean Flags have all been worked for small local markets. James Walton has reviewed these sources in a number of papers. Another interesting study by Stephen Moorhouse traces the historical development of the industry in West Yorkshire. He concludes that stone slates were carried over longer distances than is commonly believed - 20 miles is known, with a haulage cost often higher than the value of the slates. It is also apparent from records, that the early use of stone slates was not restricted to important buildings in areas where they were readily quarried but were used on the houses of all but the poorest people.
    In the less populated regions further north quarries tended to be smaller and more localized in their use. In the region around Leyburn quarries which sometimes developed into mines were operated in several of the Yorkshire Dales.  There were many quarries in Coverdale, Wensleydale around Hawes, and in Arkengathdale as well as individual examples serving the smaller communities. Hill Top Quarry in Swaledale is currently operated by Keith Brogden.
    North of the Dales there were not many quarries and there are only a few operating today. The three most important are at Shipley Banks near Barnard Castle, County Durham, Alston Natural Stone and Ladycross Quarry in Slaley Forest, Northumberland. There are some good pictures of stone roofs from Ladycross in Blanchland Village at FreeFoto.com.
    SCOTLAND To be added soon
  • Carboniferous roofs

    • The Coal Measures and Millstone Grit sandstones together have probably supplied more roofs than any other stone and they are a very important feature of both the city and rural landscapes of the north. Their large size dictates a simple roof style with few intersections or dormers. Where valleys do occur they are of the chevron type using pieces of stone cut to fit between the rakingline of the courses and sit in place without nailing or pegging. Gables are either simple sometimes with copings laid straight onto the slates or on more elaborate buildings the roof slope may butt up to a raised coping.

    Supplies of these slates have improved in recent years although there are still not enough types to suit all conservation requirements.
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