The Llewelyn Volcanic Group is an Ordovician lithostratigraphic group (a sequence of

rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

) in Snowdonia, north-west Wales. The name is derived from Carnedd Llewelyn, the highest peak in the Carneddau range where it outcrops.

Outcrops

The rocks occur across the

Snowdon Snowdon () or (), is the highest mountain in Wales, at an elevation of above sea level, and the highest point in the British Isles outside the Scottish Highlands. It is located in Snowdonia National Park (') in Gwynedd (historic ...

massif and the Carneddau and within the

Capel Curig Anticline Capel may refer to: People * Capell, surname, includes a list of people with the surnames Capel and Capell *Capel (given name), includes a list of people with the given name Capel Places England * Capel, Kent, a village and civil parish near ...

Lithology and stratigraphy

The Group comprises around 1400m thickness of ash flow tuffs, flow-banded

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

s and breccias with a variety of volcaniclastic sediments erupted or sedimented during the Caradocian epoch of the Ordovician period. The Group comprises (in descending order, i.e. oldest last): *Capel Curig Volcanic Formation *Foel Fras Volcanic Formation *Conwy Rhyolite Volcanic Formation It also includes the Foel Grach Basalt Formation and the Braich Tu Du Volcanic Formation.http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=LLV (BGS on-line lexicon of rock units)

References

Ordovician System of Europe Upper Ordovician Series Geology of Gwynedd {{UK-geologic-formation-stub