The Llewelyn Volcanic Group is an

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous ...

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

(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 ...

) in

Snowdonia Snowdonia, or Eryri (), is a mountainous region and National parks of the United Kingdom, national park in North Wales. It contains all 15 mountains in Wales Welsh 3000s, over 3000 feet high, including the country's highest, Snowdon (), which i ...

, north-west

Wales Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...

. The name is derived from

Carnedd Llewelyn Carnedd Llewelyn, also spelled Carnedd Llywelyn, is a mountain massif in the Carneddau range in Snowdonia, north-west Wales. It is the highest point of the Carneddau at and the second-highest peak by relative height in Wales, ...

, the highest peak in the

Carneddau The (lit. 'the cairns'; is a Welsh language, Welsh plural form, and is sometimes anglicised to ''Carnedds'') are a group of mountains in Snowdonia, Wales. They include the largest contiguous areas of high ground (over or high) in England and W ...

range where it outcrops.

Outcrops

The rocks occur across the

Snowdon Snowdon (), or (), is a mountain in Snowdonia in North Wales. It has an elevation of above sea level, which makes it both the highest mountain in Wales and the highest in the British Isles south of the Scottish Highlands. Snowdon i ...

massif and the

and within the Capel Curig Anticline.

Lithology and stratigraphy

The Group comprises around 1400m thickness of ash flow

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...

s, flow-banded

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

s and breccias with a variety of volcaniclastic sediments erupted or sedimented during the

Caradoc Caradoc Vreichvras (; Modern , ) was a semi-legendary ancestor to the kings of Gwent. He may have lived during the 5th or 6th century. He is remembered in the Matter of Britain as a Knight of the Round Table, under the names King Carados and C ...

ian 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