The Llewelyn Volcanic Group is an

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

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 igneou ...

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 ide ...

(a sequence of rock strata) in

Snowdonia Snowdonia or Eryri (), is a mountainous region in northwestern Wales and a national park of in area. It was the first to be designated of the three national parks in Wales, in 1951. Name and extent It was a commonly held belief that the na ...

, north-west

Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

. 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 and the second highest peak by relative height in Wales, 49th ...

, the highest peak in the

Carneddau The (lit. 'the cairns'; is a 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 Wales and England (although l ...

range where it outcrops.

Outcrops

The rocks occur across the Snowdon 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 ...

s, flow-banded rhyolites and breccias with a variety of volcaniclastic sediments erupted or sedimented during the

Caradoc Caradoc Vreichvras (; Modern cy, Caradog Freichfras, ) 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 ...

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