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  • 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
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     ROCKS AND FORMATION CONDITIONS IN THE BRITISH ISLES 
    The types of rock found in a country or a region depend on the conditions which existed when they were formed. Climate is one of the most important factors.  or example, during hot periods desert sandstones or evaporites such as salt may predominate on land, and coral reefs in shallow seas.
    mya = million years ago
     
    PERIOD BEGINING CLIMATE AND IMPORTANT ROCK TYPES
    Cretaceous 136 mya Cool and possibly arid. 
    Chalk, sandstones, clays, marls, ironstones.
    Jurassic 190 mya Warm, equable, humid. 
    Limestones including oolitic, clays, marls, shales, ironstones.
    Triassic 225 mya Hot, alternating wet and dry seasons. 
    Conglomerates, sandstones, mudstones, evaporites.
    Permian 280 mya Desert conditions. 
    Conglomerates, red breccias, red siltstones, desert sandstones, evaporites, dolomitic limestones.
    Carboniferous 345 mya Tropical. 
    Deltaic shales, mudstones, ironstones, siltstones, sandstones, seatearths, coal. 
    Marine shales, limestones, turbidites.
    Devonian 410 mya Warm, often arid. 
    Cornstones, conglomerates, red sandstones, red marls.
    Silurian 440 mya Warm. 
    Marine, shelly, graptolitic and calcareous, shelly rocks, reefs, greywackes.
    Ordovician 530 mya Moderate to warm. 
    Mainly marine, grits, greywackes, conglomerates, sandstones, shales (slates), mudstones, cherts.
    Cambrian 570 mya Equable, marine. 
    Marine conglomerates, sandstones, shales (slates), flags, greywackes, limestones.
    Pre Cambrian 4,000 mya .
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