NM4862 : Cone Sheets and Sgeir Mhaol

taken 4 years ago, near to Kilchoan, Highland, Great Britain

Cone Sheets and Sgeir Mhaol
Cone Sheets and Sgeir Mhaol
Sgeir Mhaol is the low ridge of rock just offshore. The name means something like 'bald skerry'. To the right of the pool are some cone sheets, dipping to the west.
Cone Sheets
Cone sheets are formed by magma penetrating arcuate cracks around the centre of a volcano as it subsides. Unlike ring-dykes, which dip outwards, cone sheets dip inwards towards a central point or focus.

West of Mingary Pier is a series of cone sheets which is one of the best examples, if not the single best example, in the world; a geological locality of international importance.

There are two swarms of cone sheets associated with Centre 2 of the Ardnamurchan volcano, one swarm older than the other. The individual sheets are quite thin, few being more than 6 metres thick, but adding them all together their total thickness is about 1300 metres - which gives an inkling of how numerous they are.

The cone sheets exposed west of Mingary dip at angles of about 35 to 45 towards a focus somewhere near Sonachan. They are mainly composed of quartz-dolerite or basalt, though some are composite and a few felsic sheets do exist. They cross, join and split off from one another, and are cut by later basic dykes.

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NM4862, 6 images   (more nearby )
Photographer
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Date Taken
Saturday, 14 September, 2013   (more nearby)
Submitted
Tuesday, 17 September, 2013
Geographical Context
Coastal  Geological interest  Islands 
Subject Location
OSGB36: geotagged! NM 4882 6279 [10m precision]
WGS84: 56:41.3467N 6:6.2127W
Camera Location
OSGB36: geotagged! NM 4899 6299
View Direction
Southwest (about 225 degrees)
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