Geology Rocks on the Isle of Mull
Whether you’re a keen geologist or just interested, there is no doubt that geology fascinates.
These geological sites are simply the author’s choice of interesting places to visit. They are listed in the order of an itinerary, starting at Tobermory, travelling west and south and ending up in Iona.
1. ‘S Airde Beinn
‘S Airde Beinn, near the Mishnish Lochs just west of Tobemory is a volcanic plug, composed of a rock called dolerite, the worn down stump of a magmatic conduit which probably supplied much of the lava that makes up the surrounding area. It is of early Palaeogene age (60 million years old – what used to be known as the Tertiary). It is NOT a volcano. The summit hollow is filled with a loch (Lochan ‘S Airde Beinn) which is probably the result of glaciation. A great viewpoint on a good day.
2. Calgary Bay Dyke
Near the pier at Calgary Bay there is an obvious dyke running down the hillside. Part of this has been used as a wall on the now derelict boathouse! It is one of the best examples of a dyke to be seen in Mull. Like most of the Mull dykes it runs NW-SE and dates back to the early Palaeogene era, 60 million years ago.
3. Laggan Ulva Ash bed and dykes
Near Lagganulva, there is a very fine outcrop of volcanic ash deposits. Most of the ash localities are hard to get to but this one is only 5 minutes from the road. The ash was laid down early on at the beginning of the Palaeogene volcanic episode and appears to contain all sorts of shards, volcanic bombs and unsorted material. It is criss crossed by numerous dykes and these have affected the ash giving it a very distinctive red colour.
4. Ulva Basalt Columns
Ulva like Staffa has a great location for seeing columnar basaltic lava. It is on the south side of the island, about 45 minutes walk from the pier. These columns are very similar to the ones at Staffa but are a lot more accessible. Best visited at low tide.
5. Loch Ba Ring Dyke
The Loch Ba Ring Dyke represents an upwelling of molten rock that filled the ring fracture of a collapsed volcano. It has been described in the literature as “most perfect example of a ring dyke known to science”. It rises like a wall of rock above Loch Ba and up the slopes of Beinn a’ Ghraig. It is also seen on the other side of Loch Ba. The rock of which it is composed is interesting as it is a mixture of both granitic and basaltic magmas, two very different rock types.
6. Loch na Keal P-forms
P-forms are channels cut into the rock by glaciers. On the south shore of Loch na Keal near Knock are some very good examples of these. These P-forms are reckoned to be the best to be seen in the whole of the UK. Very easy to see as they are right beside a parking area!
7. Gribun unconformity
At Gribun, there is a great example of an unconformity – a place where two beds of rock are found in contact but where there is a huge age difference between them. In effect , there is a big age gap between the two beds of rock. This is well seen at Gribun where Moinian strata of approx 1 billion years of age is directly overlain by Triassic rocks of about 250 million years of age. The difference is accentuated by the fact that the underlying Moinian rocks are dipping at about 40 degrees whereas the Triassic rocks above are horizontally bedded. A classic site and almost as good as the historically significant “Huttons’s Unconformity” at Siccar Point in Berwickshire.
8. Mackinnons Cave
Mackinnons Cave is just down the coast from Gribun – it is tidal so take care! The cliffs here are spectacular as is this whole part of Mull called the Wilderness.
9. Wilderness
The Wilderness is an amazing place of sea stacks, arches, caves and towering cliffs. In places the ground is rent by deep fissures. This is not an easy place to visit involving a long trek over difficult ground and requiring good scrambling skills and a head for heights. Most of the rock is made up from Moine psammites, similar to those found at Gribun, but Mesozoic sedimentary rocks are also found. Good fossils abound.
10. Staffa
Staffa is one of the geological wonders of the world, not just Mull and its associated islands. The basalt columns and Fingals Cave have been a popular tourist attraction for hundreds of years. The name was originally An Uamh Bhinn” menaing “melodious cave” from the sound of the waves. The Gaelic for “Fingal’s Cave” is Uamh Fhinn which sounds very similar. Staffa is a fascinating place to visit – one trip is never enough!
