Mull Geology

Today was looking good weather wise so it was a good opportunity to get back down Loch Buie  / Loch Uisg way and spend some time wandering looking at rocks!  It was a while since I had been up at the area that formed a major part of my MSc so a bit of re-aquaiting was needed The Gleann Beag Intrusion (as I referred to it) is unusual - it is picritic, very fresh, contains huge amounts of olivine, the olivine is highly magnesian, up to 91.5 % Forsterite and the rock in many places displays tremendous layering. There are other neat features as well as the pictures will show. On the BGS map, the intrusion is shown as a sinuous dyke of the Mull Swarm but there is more to it than that. Anyway, here are a few pics of the trip. These are only a few of the total number of photos I took, just to give a flavour of what the rocks look like: Loch Uisg, looking serene Its a bit of a haul up by the Allt a'Bhacain Seilich but it gets you to the high ground of the Laggan Peninsula

Dr John Faithfull had emailed some interesting photomicrographs of what was reported as being from a sill near Torrans in SW Mull. The slides show broken plagioclase and cpx crystals that look like they are from something explosive. According to the info I had, it was from a sill. Since I had a bit of time and was in the area. I decided to have a look to see if I could find the original location The Grid Ref I was given was NM499241 and near a waterfall. There are several waterfalls in this area. Here are the first, just next to a rough track The sill is obvious with the waterfall running over it. I took a sample of the rock but it doesnt look too exciting - looks pretty typical of dolerite sills The top waterfall / sill in close up The other sill is just below it. Got a sample of this as well and it doesnt look an awful lot different There is another waterfall in the general area, just downstream a bit:

There are several volcanic plugs around North Mull, the most notable being 'S Airde Beinn.  These plugs are reckoned to be conduits through which magma flowed, to pour out onto the surface as lava flows. There are two plugs marked on the BGS map near Loch Frisa at a location called An Sgriodain. I had been to them before and was discussing them on Twitter just a few days ago. The weather was nice so it seemed a good place for an afternoon stroll. Loch Frisa looked impressive. Speinne Mor is the prominent hill in the distance. Loch Frisa runs NW -SE like so much of the geographical features of Mull. Most of the dykes run in this direction as well, a reflection of the tectonic regime that was happening all these years ago during Palaeocene times. The two plugs are not far from where the picture was taken. The first is high up on the hillside. Here is a picture from a few years ago - I didnt make it up there today as I was more interested in looking at the other one.

Had a visit to Ulva today. Ulva has been in the news a lot recently because of the Community Buyout. I had been planning to visit it for some time to recce the route for a geology walk and the weather forecast was good for today. The geology of Ulva is really neat, the basalt lava columns on the south side are second only to those on Staffa - its the same rock formation - the "Staffa Lava Formation" There is also, according to the BGS map some mugearite and ash on the north side near the church but vegetation and poor access makes that a bit of a challenge! Maybe some other day - todays walk was to the famous basalt columns. Its not too far from the ferry slipway - about 30 - 40 minutes walk but well worth it! Here are the pics with brief descriptions: The Telford Church on Ulva - the pyramid in the grounds is a war memorial for WW1 - four mens names on it Tremendous skies looking over towards Mull Beyond the main outcrop of the basalt columns, a view to the w

Had a little bit of time today while down in Iona doing some other work, and as the weather was good it seemed a good opportunity to go out and have a look at the north end of Iona for a change. I havent spent as much time in this part of the island as I have in the south so it felt like a good chance to do some familiarisation. Last time I was at the north end was last year, with Brian Upton for a quick rake around and to talk rocks! No esteemed company today unfortunately! The sea views are great: Looking north Stac Mhic Mhurchaidh in the distance there, behind Eilean Chalbha. SMM is a columnar dolerite, probably of Palaeogene age, Eilean Chalbha like most of Iona is Lewisian so much older What I really wanted to look at was the "basal conglomerate at the base of the "Iona Group" rocks. The Iona Group used to be described as Torridonian but modern research tends to suggest the term "of Torridonian affinity"