Llandeilo Group

Source: Wikipedia, the free encyclopedia.

In

volcanic
rocks are intercalated.

Features

A remarkable feature in the history of the Llandeilo rocks in Britain, more especially in

Builth and in Pembrokeshire. The average thickness in Wales is about 2000 ft. The group is usually divided in this area into three sub-divisions. In the Corndon district of Shropshire the Middleton Series represents the Llandeilo group; it includes, in descending order, the Rorrington black shales, the Meadowtown limestones and flags, and the western grits and shales. In the Lake District the great volcanic series of Borrowdale, green slates and porphyries, 8000 to ooooft. in thickness, lies on this horizon; and in the Cross Fell area the Milburn beds of the Skiddaw slates (see Arenig
) appear to be of the same age. In Scotland the Llandeilo group is represented by the Glenkiln shales, black shales and yellowish mudstones with radiolarian cherts and volcanic tuffs; by the Barr Series, including the Benan conglomerates, Stinchar limestone and Kirkland sandstones; and by the Glenapp conglomerates and Tappinsrnudstones and grits south of Stinchar. Graptolitic shales, similar to those of southern Scotland, are traceable into the north-east of Ireland.

Fossils

The fossils of the Liandeilo group include numerous

pteropods. The cephalopods are represented by Orthoceras and Cyrtoceras
.

Quarrying

The green roofing slates and plumbago (graphite) of the Lake District are obtained from this group of rocks.

References

 This article incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). "Llandeilo Group". Encyclopædia Britannica. Vol. 16 (11th ed.). Cambridge University Press. p. 828.