Pre-Cambrian (>540 million years)
Britain's oldest geological strata are Pre-Cambrian in age and outcrop in only a few limited areas of Britain. The most extensive outcrops occurring in Scotland, Anglesey, Church Stretton and Charnwood. Though commonly used in local vernacular buildings there has been only limited commercial production of building stone from these rock units. In general the outcrops in Scotland are too remote from their potential markets to have been widely exploited. However, the thick blue-grey slate with their characteristic coarse pyrite concretions, known as the Ballachullish Slate, quarried on the shores of Loch Leven, from the Dalradian (Ballachullish Slate Formation) and used throughout Scotland in the 19th and early 20th centuries, were a significant exception (Fairweather 1974). Other slate beds in the Dalradian were worked nearby at Easdale, and further afield at outcrops along the Highland Boundary Fault, the Aberfoyle slate belt and also in the Aberdeen-Banff successions (Richey & Anderson 1944; Tucker 1976; Brumhead 19??). All these Scottish slate producers suffered badly from the competition of the Welsh producers and were eventually forced to close.

Swithland slates
 

Lower Palaeozoic (540-417 m.y)
Cambrian, Ordovician and Silurian Lower Palaeozoic rocks outcrop extensively in the west of Britain in Wales, Cumbria and the Southern Uplands areas. These rocks units have supplied sandstones, slates and limestones for local vernacular housing for centuries such as the Horton Flagstones from Ribblesdale in Yorkshire and the numerous Shropshire quarries supplying various stones to Shrewsbury (Mitchell1985; Scard 1990).

Splitting roofing slate at Penrhyn quarry Gwynedd
 

Elsewhere in Britain slates have been produced commercially from the Ordovician rocks at the Burlington, Tilberthwaite and Honiston quarries in Cumbria (Geddes 1975). These slate quarries were widely renowned long before the boom in Welsh slate production. The heavier 'Westmoreland' green slates were widely used on prestigious buildings throughout the country before being displaced by the thinner and lighter Welsh slates. Several slate quarries are still operational in the area.

Cornish rag slating St Mabena
 

Devonian sandstone flagging and sets. Stromness, Orkney
 

In Scotland the Devonian succession has yielded abundant sandstone for building particularly in the Dundee area. In the 19th century numerous quarries were known to have worked the reddish sandstones (Mackie 1980). Good access from these quarries to the coastal ports lead to a flourishing market in England, Europe and even North America and Australia for much of the late 18th and 19th centuries. The most successful quarries were probably those at Carmyllie with its fine, bluish-green, sandstone being shipped extensively overseas, notably for paving in Cologne Cathedral (Mackie op. cit.).

Further north the thinly bedded Devonian sandstone successions in the well known quarries around Thurso in Caithness have provided paving stone for centuries to many towns and cities in Britain, Europe and America. Omand & Porter (1981) list 43 towns and cities in England alone, which the quarries had supplied with flagstones by 1877. They also show exports from the quarries to Australia, India, New Zealand and even South America. The dark grey to black, fine grained sandstones have been used to constructing vernacuiar buildings for centuries, commercially, however, the flagstone industry developed extensively in the 19th century and has, after a period in the doldrums this century, has now become a flourishing industry once again.

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