Silurian Period

(443 – 419 million years ago)

The big story . . .

At the start of this period of geological history, the lands that would eventually become Wales and England lay within the eastern part of a micro-continent which we call ‘Avalonia’.  It lay far to the south of the Equator, separated by an ocean we call ‘Iapetus’ from a large continent – ‘Laurentia’ – to its north.  Scotland was a part of this more northerly continent along with Greenland and much of North America.

During the Silurian period Eastern Avalonia together with Baltica collided to form a larger continent which we call ‘Laurussia’.

This collision caused a huge range of mountains to be thrown up where the two land-masses docked.  Geologists refer to this period of mountain-building as the ‘Caledonian Orogeny’.  The mountains of modern-day North Wales, the English Lake District and Scotland are but the eroded ‘roots’ of this former mountain chain, now referred to as the ‘Caledonian Mountains’, and which may have reached Himalayan proportions.

The rock legacy . . .

Rocks of this age are found in the western area of the Geopark.  They are mostly mudstones, siltstones and sandstones, some of which were deposited in deep water on the continental shelf.  Others were deposited in shallow water as the ripple marks preserved in them suggest.

Silurian rocks of the Geopark

Silurian rocks of the Geopark

The rocky bed of the Sawdde Gorge which is followed by the A4069 Llangadog – Brynaman road offers a good chance to view this succession of rocks which all dip steeply to the southeast in this area.

Rock layer/s Description Approximate thickness
Raglan Mudstone Mudstones/siltstones and some sandstones 1100m
Temeside Mudstone Muddy siltstones with some sandstones Up to 50m
Tilestones Sandstones 15 to 35m
Cae’r Mynach Mudstones, siltstones and sandstones 155 to 260m
Fibua mudstones 40 to 170m
Trichrug Muddy sandstones Up to 20m
Mynydd Myddfai Sandstone Sandstones with some conglomerates Up to 30m
Aberedw Muddy siltstones and sandstones Up to 80m
Hafod Fawr Mudstones, siltstones and sandstones Up to 710m
Cwm Craig Ddu Mudstones, siltstones and sandstones 70 to 425m
Irfon Mudstones and siltstones Up to 120m
Halfway Farm Mudstones, siltstones and sandstones Up to 105m
Sawdde Sandstone Mudstones, siltstones and sandstones Up to 660m
Tirabad Mudstones, siltstones and sandstones Up to 740m
Llangammarch Mudstones and siltstones Up to 500m
Builth Mudstones mudstones Up to 260m
Cerig Mudstones, siltstones and sandstones 750m
Derwyddon Sandstones 25 to 75m
Cefngarreg Sandstone Sandstones with mudstones Up to 400m
Trefawr mudstones Up to 200m
Crychan Sandstones Up to 170m
Bronydd mudstones Up to 275m
Chwefri Mudstones and sandstones Up to 750m
Garth House Mudstones and sandstones Up to 90m
Cwm Clyd Sandstone Sandstones Up to 10m

View the Silurian Timechart.

What’s in a name?

The name of this geological period comes from that of the Silures tribe whom the conquering Romans found living across much of South Wales.  The name of Llandovery is also known to geologists across the globe as the town has given its name to Silurian rocks of a certain age throughout the world.

this section of the site is still under development – a photo of Blue Quarry in Sawdde gorge, showing ripple marks will appear here