//Ordovician Volcanic Rocks

Ordovician Volcanic Rocks

Pillow Talk

Between 440 and 490 millions of years ago volcanic islands characterised the ocean which covered Wales in the Ordovician Period. The volcanic eruptions, mostly beneath the sea, gave rise to flows of lava rich in magnesium and iron.

As the extremely hot tongues of lava came into contact with cold sea water the outer surface hardened, forming a hard crust around the centre of liquid lava.

Then as the lava split, the blobs of lava piled up on top of each other, forming ‘pillows’.

See the rarities

Some of Wales’s rarest mountain plants grow on the mildly acid soils that developed on this lava. Our ‘Conserving Our Future’ area, a short walk from the Stable Block restaurant, has a great display of these plants.

Strange But True

A very odd lichen grows on these rocks. Most lichens are made up of a fungus and an alga or bacteria. But the pink bull’s eye lichen Placopsis lambii has all three life forms in one body, and it produces strange red blobs when it fruits.

The NBG's Ordovician Volcanic Rocks come from ARC Builth [Llanelwedd] Quarry, PowysWhere do the boulders come from?
ARC Builth [Llanelwedd] Quarry, Powys


475 million years old

Ordovician Volcanic Rock at the NBG

A volcano erupting
A volcano erupting

Lava solidifying
Lava solidifying

Purple saxifrage
Purple saxifrage

Bull's-eye lichen
Bull’s-eye lichen Placopsis lambii

'monster' lichens on Ordovician Dolerite
Lichens on Ordovician Dolerite