Sill is a Geological term for an Igneous intrusion between layers of older rocks.
The prominent Tors visible along the North Pembrokeshire coast (eg. Carn Llidi,
Carn Penberry, Garn Fawr) are Volcanic (Igneous) intrusions - mostly sills -
formed when molten magma pushed its way between other sedimentary layers of
mud and ash on the ocean floor.
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At this location ("Ogof Golchfa") two bands of vertical rock strata are separated by a
band of rock - (Sill ) - many metres wide.
The rocks are covered with Lichens , but some bare surfaces can be found exposing an
Igneous rock with quartz and feldspar crystals (microtonalite).
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A Raised Beach can also be seen at this location .
Ref: 6681
Date: 02/04/2010
Location: SM 740.236
