Stromness Flagstone Quarries

Overview

Devonian lakebed siltstones split so cleanly into flat, durable slabs that they paved and roofed Stromness itself, worked from numerous small quarries across West Mainland Orkney.

History

The Stromness Flags take their name from the town they helped build: flagstone used to construct Stromness itself was quarried from the shore at the Point of Ness nearby, and the same beds were worked in numerous small quarries across West Mainland Orkney for paving flags and roofing slates. The rock's fine, even bedding — laid down as mud and silt accumulated in a vast Devonian lake around 387 million years ago — let it be split into thin, tabular slabs ready-made for paving without heavy dressing. Today only the Quoyloo quarry remains active, though modern extraction yields fewer of the well-preserved fossil specimens the formation is also known for; historic flagstone from an old, reopened Orkney quarry has more recently been used to match existing paving during restoration work in Stromness itself.

Geology

The Stromness Flags are grey and black, thinly bedded and in part laminated dolomitic siltstones, shales and subordinate very fine sandstones, part of the Middle Old Red Sandstone sequence deposited in the ancient Orcadian Basin lake during the Devonian period. The sequence comprises more than fifty rhythmic cycles, each recording a lake-level change from deep, fish-rich water through shallow desiccating conditions to river-deltaic sediments, and includes the striking fossil algal reefs known as the 'Horse-tooth Stone' at Yesnaby.

Workings

Worked from numerous small quarries scattered across West Mainland, splitting the rock along its natural bedding planes into flat slabs requiring little further dressing.

Closure

Most of the historic small quarries have long fallen out of use; only the Quoyloo quarry remains active today.

What remains

The Quoyloo quarry remains active; the many smaller historic workings across West Mainland are disused.

Flagstone from these quarries survives widely in Stromness's own paving and building fabric, with historic stone periodically reused in restoration work.

Abandoned workings can be dangerous — unstable ground, uncapped shafts, flooding and bad air are common even where a site looks safe from the surface. This entry describes history and general location only; it is not an access guide.

Recorded claims

Individual factual claims, each attached to the source(s) that support it below. Where sources disagree, both are kept.

• Flagstone used to build Stromness itself came from the shore at the Point of Ness; the same beds were worked in numerous small quarries across West Mainland for paving and roofing. ¹
• The Stromness Flags are dolomitic siltstones and shales laid down in the Orcadian Basin lake during the Devonian period, in over fifty rhythmic cycles recording lake-level change; only the Quoyloo quarry remains active today. ²

Sources

1. (primary) Stromness Flagstone — Building Stone Database Scotland (British Geological Survey)
2. (primary) Middle Old Red Sandstone of Orkney, Stromness Flags — British Geological Survey (Earthwise)

Record created: 27 August 2026 · Last researched: 27 August 2026