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'S Airde Beinn. Even the name is evocative. Why isnt it "A' Bheinn as Airde" if the name really means the "highest mountain"? A fascinating little hill and an absolute classic of the type of hill that isnt all that high, but has tremendous character. Munros? Pah!

Anyway, I was sort of near it, and round it, but not quite "up on it" today - maybe later this week when the weather is better. Its not a big deal anyway, 40 minutes to go up and down including all the way round the top of it.

So what makes it special?

First let's look at a popular misconception: SAB is a volcanic plug. It is NOT a volcano per se - it is an example of a feeder system for the lava flows that cover north Mull. It is well described in the Mull Geological Memoir. So why does it have a crater? Well, it would be nice to think of it erupting and building up like some sort of Mull version of Fujiyama, but the reason is a bit more prosaic than that.

The "crater" is actually a glacial depression, filled with water (Lochan S Airde Beinn). A geological fault runs all the way through it, and this has probably provided the line of weakness which was gouged out by the glaciers, and is now filled with water.

The rock itself is a very coarse dolerite, the same sort of material that makes up the rocks that Edinburgh and Stirling Castles stand on. SAB is actually a very important geological site - it gets listed in the governments Geological Conservation Review papers and web site. If you want to know more, a lot more, try this:

http://www.thegcr.org.uk/Sites/GCR0021.htm

Numerous other Mull sites are listed in the GCR, such is the importance of the island to igneous petrology.

So the next time you are up there, just stop and think, you are on top of something quite special - but I think you knew that anyway! Pics below:

Now how about a real close up view of this place? These wide angle shots are all very well, but what really lies beneath your feet?. REAL close up as in 30 microns thick, under a geological microscope, in plane polarised light:

And the same stuff again, this time in crossed polars, looks quite coloirful doesnt it? Amazing how a dull looking piece of rock can appear when ground thin and seen through the microscope:

Many, many thanks to Rob of Geosec Slides in Spilsby, Lincs, who visits regularly and makes thin sections of rocks like these. Some rocks are truly amazing under the microscope. Rob has an Ebay shop where he sells these slides: http://stores.ebay.co.uk/Geosec-Slides, These 2 pictures of the rock in thin section are HIS, not mine, by the way!

Mountainman