Moel yr Ogof is a summit 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 nam ...

. It is a subsidiary summit of

Moel Hebog Moel Hebog (Welsh for ''Bare Hill of the Hawk'') is a mountain in Snowdonia, north Wales which dominates the view west from the village of Beddgelert. It gives name to a whole range of peaks in the north-western corner of Snowdonia, which i ...

and a sister peak to the lower Moel Lefn. There is an

asbestos Asbestos () is a naturally occurring fibrous silicate mineral. There are six types, all of which are composed of long and thin fibrous crystals, each fibre being composed of many microscopic "fibrils" that can be released into the atmosphere b ...

trial mine located on the summit. A small seam of white asbestos was discovered however insufficient amounts to commercially mine.

Geology

The summit of Moel yr Ogof is composed of a brecciated

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 ...

, diagnostic of gravitational collapse in a rhyolite dome. Surrounding the crown of the mount is a geological unit consisting of alternating bands, of varying thickness, of

pillow basalt Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...

s and a green/grey

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

that is of

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

origin, potentially derived from the pillow basalt itself. The pillow basalt is relatively well preserved in places, where

devitrification Devitrification is the process of crystallization in a formerly crystal-free (amorphous) glass. The term is derived from the Latin ''vitreus'', meaning '' glassy'' and ''transparent''. Devitrification in glass art Devitrification occurs in glass a ...

rims clearly outline the individual pillows. It is composed of dark green/black, very fine crystalline, basaltic rock, which has weathered to a dark red/brown colouration due to the presence of iron minerals. The sandstone member of the unit is a pale green/grey, fine to medium grained, well sorted sandstone. It shows good cross-bedding and rare ripple structures indicating a tidal depositional environment. There is a large scale

syncline In structural geology, a syncline is a fold with younger layers closer to the center of the structure, whereas an anticline is the inverse of a syncline. A synclinorium (plural synclinoriums or synclinoria) is a large syncline with superimpose ...

running NNE-SSW, that extends straight through the summit of Moel yr Ogof and can be seen clearly, in the mountain's profile, when taking the path up to the Hebog ridge from the South.

Owain Glyndŵr Owain ap Gruffydd (), commonly known as Owain Glyndŵr or Glyn Dŵr (, anglicised as Owen Glendower), was a Welsh leader, soldier and military commander who led a 15 year long Welsh War of Independence with the aim of ending English rule in Wa ...

cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...

can be found on the cliff at the eastern flank of the mountain. The Beddgelert Forest lies directly to the north east, while Cwm Pennant lies to the west. Good views of the

Nantlle ridge The Nantlle Ridge ( cy, Crib Nantlle) is the name given to a small range of mountains in Snowdonia, north Wales which runs south-west from the village of Rhyd Ddu for a distance of about , ending above Nebo in the Nantlle Valley. The Nantlle Ridg ...

to the north are observed.Nuttall, John & Anne (1999). The Mountains of England & Wales - Volume 1: Wales (2nd edition ed.). Milnthorpe, Cumbria: Cicerone. .

References

External links

www.geograph.co.uk : photos of Moel yr Ogof and surrounding area
Moel yr Ogof (view from Moel Hebog)

Beddgelert Dolbenmaen Mountains and hills of Gwynedd Mountains and hills of Snowdonia Hewitts of Wales Nuttalls {{Gwynedd-geo-stub