to the Isle of Eigg with Geowalks
Saturday: Arrival and Introduction to Eiggs Geology
Well what can I say? It was eiggxhilerating, eiggxciting, eiggxtraordinary and an eiggceptional eiggxcursion that left me feeling eiggstatic. What an eiggxcellent eiggxperience and that is said without a word of eiggxaggeration. A wonderful island to eiggxplore with eiggxpert, Angus Miller, to eiggxplain the geology. Okay, okay that is enough! Well not quite; the trip eiggxceeded all my eiggxpectations and I would like to eiggxpress my eiggxuberant thank you Angus for a wonderful four days.
I had set my alarm for 0430 hours but did not surface until 0450 hours and had a mad rush to meet Angus and Bill by 0600 hours in Leith. The journey to Arisaig was made in the record time of 3.5 hours thanks to Bills excellent driving; no not eiggxellent , I am not going there again, the first paragraph was enough! We all arrived in good time with glorious sunshine and a smile on everyones face. We boarded the Shearwater ferry that left promptly at 1100 hours and when we thought that we would be at our destination before long a detour was made as porpoises had been sighted. Fantastic! I have never seen porpoises before and there were perhaps half a dozen to be seen. A couple were so close that I heard them expel air. All too soon the spectacle was over and we resumed our route towards Eigg.
As we arrived at the pier to disembark the sound of the bagpipes could be heard. It sounded real! It was real as a piper played on the shore to welcome us; what a perfect greeting!
After placing our luggage in a trailer for Karen Helliwell to take to the Glebe Barn Field Centre where we were staying for three nights and a short visit to the café and shop we started on our first geology walk of the trip but not until after we had our picnic lunch at a white sandy bay, Poll nam Partan. It was whilst having our very relaxing lunch that a couple of us noticed the tiny plant growing around us. The petals were so small that a geological magnifier was used to count them! That evening the plant was identified as cornsalad or lambs lettuce.
To put it in a nutshell the Isle of Eigg is largely formed of lavas with the ridge of An Sgurr dominating the skyline giving enthusiastic geologists a beckoning call to discover as much geology as possible. The island interested the pioneering Victorian geologist Hugh Miller to make investigations when in 1844 in support of his friend, the Rev. John Swanson, Minister of the Small Isles he visited Eigg. His most remarkable discovery was of the bones of a plesiosaur, together with other fish and reptilian remains.
As a general introduction; Eigg is part of a group of islands known as the Small Isles and includes Rum, Eigg, Muck, Canna and Sanday. About 62 million years ago, during the Tertiary, quiet conditions were rudely awakened by the sudden eruption of ash on the west coast, followed by basalt lavas flowing over the land surface of what is now the Inner Hebrides. This event was the final opening of the North Atlantic Ocean, as Scotland separated from North America. The Eigg lavas poured over a landscape of Jurassic and Cretaceous sedimentary rocks, forming a shield that, thanks to its relative toughness preserved the older sedimentary rocks beneath. The lavas stopped about 55 million years ago. The climate was warm, varying from humid to semi-arid, as revealed by the red fossil laterite soil horizons between the lava flows, testimony to deep tropical weathering.
Weathering and erosion of the lava piles has picked out the relatively weak bases and tops of flows, forming ledges producing the terraced hillsides known as trap topography. It is the most widespread landform on Eigg.
The Sgurr is the most prominent landscape feature and represents a surface flow of highly acidic lava, now black glassy pitchstone with superb radiating cooling joints. This lava flow filled a valley excavated into the older basalts. Subsequent erosion removed the surrounding weaker basalt lavas, to produce a positive feature in the form of the very hard and resistant pitchstone. This is an example of inverted topography; what was a valley is now a ridge.
Dating of the Sgurr pitchstone has shown that, at 53 million years old, it is the youngest of the Hebridean volcanic rocks. Near the top of the flow of pitchstone, where the lava was acted upon by irregularly percolating water, complex cooling formed joints in spectacular fans. It is thought that soon after the joints in the Sgurr formed, more magma intruded the pitchstone body from below, producing sill-like layers within it.
Well that is enough of the heavy stuff! After our lunch we continued walking northwards where the path took us below impressively large basaltic columns forming the ridge of Druim an Aoinidh.
These belong to the lowest major lava flow, which is thick and columnar over much of the island. Still walking northwards across fields we came to the cliff-top at Bealach Clith. Here a muddy path descended the cliff and following the path; the basalt cliffs became higher above us showing fine columnar jointing and at this location we had our first exposure of the Valtos Sandstone Formation. The following is a description of the sandstone from the booklet The Geology of Eigg by John Hudson and Ann Allwright purchased at the shop. An excellent buy; a must have and worth every penny at £5. The sandstone record a great influx of sand, forming deltas built into the Jurassic lagoons that then occupied the Minch area, this sandy episode had its counterpart in north Skye, whence the name Valtos Sandstone Formation for these rocks. The sand had its source in hills that were roughly where the Scottish mainland now is, as deduced from larger pebbles found among the sand, and minute sand-sized grains of distinctive minerals originating from metamorphic rocks like those of the Highlands. We then studied in more detail a cliff that had a Mugearite sill on top of basalt columns that was on top of the Jurassic Sandstone. Bisecting the basalt was a further sill. A few hardy members of the group continued along the shore to study the exposures of Jurassic shales and thin limestones and came back with a few fossils. One find was a very well preserved small mussel-like shell Praemytilus strathairdensis still showing the mother-of-pearl structure.
Our route back was via the Chapel of St Donan thought to be a 16th century construction but there is evidence of earlier religious settlement in four cross slabs which date from the early medieval period. St Donan, an Irish missionary, was martyred by either Viking raiders or the local queen in 617 or 618.
Sunday: Laig Bay and the Singing Sands
Sunday was our day for visiting Laig Bay and the Singing Sands on the west coast of Eigg. These are two beautiful sandy bays, and the excursion would also include cliffs of Jurassic sandstone with fantastic concretions and spectacular views of the Rum Cuillin. Before setting off in glorious sunshine, a male hen harrier flew by that was to be seen a couple of more times on our walk to the bay. This was another first for me! We approached the bay from a cliff top having walked through Blar Dubh a very pleasant forestry plantation.
As we walked through the gap in the cliffs we all had a jaw dropping moment with gasps of awe at the spectacular view before us. The panorama was absolutely magnificent. In the distance could be seen the cliffs of Beinn Bhuidhe towering above Cleadale showing clearly landslides where whole segments of cliffs had rotated and then subsided. These cliffs are crumbling and on a still day this action can be heard. I am not sure that I would like to be living in Cleadale! Also very clearly seen was a raised beach surrounding Laig Bay and in the foreground a kettle hole lochan. Kettle holes are formed when thick glacial till is deposited as a glacier retreats. Masses of ice may be included within this till and when these melt depressions form on the surface that may fill with water and a better example of this I doubt could be seen anywhere else!
The path descended to the shore of Laig Bay with the lochan on our right. As the tide was out we were able to appreciate the wide expanse of sand that was very white due to its composition being of shell fragments as well as some quartz grains. Beautiful patterns were made on some areas of the sand (southern end) where dark basalt grains lay in contrast to the overall white appearance.
As we walked across the bay the most perfect views of the Rum Cuillin were to be seen and it was explained to us that between the two islands was the line of the Skerryvore-Camasunary Fault. This is a major fault a zone along which movement has taken place. This was initiated, along with other faults, at the end of the Caledonian orogeny. The effect of the movement was upwards on the Rum side of the fault, thus raising the older rocks of Rum to the same level as the younger rocks of Eigg.
To the north of Laig Bay the cliffs of the Valtos Sandstone start. As the tide was low we were able to follow the shore all the way to the Singing Sands Bay (Camas Sgiotaig). The following photographs show cliff scenery, one of the many intriguing dykes with its baked margins, a natural arch and concretions galore!
It is worthwhile noting that calculations have been made indicating that a concretion 50cm across would have taken about 3 million years to grow!
Eventually after all the excitement of the varied formations of the concretions we reached Singing Sands via a natural arch in sandstone. Interestingly, to quote from The Geology of Eigg, The term dyke originates from instances where vertical basalt dykes have been intruded into soft sediments or lavas, and erosion leaves them standing proud. However, at Laig Bay, the reverse is the case: the most resistant rocks are the baked sandstones of the dyke margins; the sandstones away from the dykes are of intermediate resistance, and the most eroded rocks are the basalt dykes themselves.
I am afraid that I do not have any photographs of the Singing Sands simply because I was having so much fun playing. In fact after the storms of 2005 a lot of the sand disappeared but there were some areas where the magic was still there. A couple of us ended up sand dancing to the squeaky sounds made by scuffing our feet on the dry sand. Has anyone a photograph of the dippy two? We also experimented sweeping our hands across the sand to make the sound and were successful. A little to the north of Camas Sgiotaig we managed to find, in the sandstone, fossil driftwood in the form of charcoal, testifying to wildfires of Jurassic times. The wildfires could have started by lightning, but some of it may also have resulted from volcanic activity.
After discussion different routes were decided for the rest of the day. I ended up joining the group climbing up over Blar Mor then via Guala Mhor, Leit an Aonaich and Dunan Thalasgair to reach the top of Beinn Bhuidhe (340m). I hasten to add we stopped for lunch half way up. It was in the area of Guala Mhor that it was pointed out to me that there were green hairstreak butterflies. Well that was it; I just had to stop to see my first. It was very difficult as the butterflies were extremely active but eventually I had the most perfect view. After that I seemed to see them where ever I went on Eigg. Thank you Peter; I would have missed them if it were not for you.
Whilst having lunch we did a spot of birdwatching. Vicky and I spent ages watching a particular bird and could not decide what it was. I have come to the conclusion that it was a buzzard, a very pale form, as I saw one in the same light the following weekend in Dalkeith Park with almost the same markings but not quite such dark armpits. We also had the pleasure of seeing a peregrine falcon stooping.
On the last leg of the climb and in amongst the rocks I saw a few cushions of moss campion; another first. They were past there best which was interesting as they are not supposed to be flowering until June-August. Thats global warming for you!
Once recovered from our climb the walk along the top of Beinn Bhuidhe gave us splendid views and was easy going for as long as there was a path to follow! It was once the path disappeared that the going got really tough and it was only after we managed to get back to the road near the school that we were able to relax once more. We were informed that there was a path down into Cleadale from the top but, unfortunately, we did not see it. I recommend that the whereabouts of the path be found out for those who tackle this route in the future for I am sure that it would make the experience more enjoyable. Unfortunately, the path is not marked on the OS Explorer 397 map. Having said this I would not have missed out on this adventure.
Below the slopes beneath the Sgurr are the ruins of two villages Grulin Uachdrach and Grulin Iochdrach deserted during the Highland Clearances during the 19th century. We had time for a short visit to these villages that had a sombre air about them even in the sunshine.
The final part of our excursion today was to visit the Massacre Cave and Cathedral Cave on the south coast. Situated in the heart of Clanranald country, the island found itself involved in every MacDonald rebellion against the Crown and in a good many feuds. A lengthy feud between the MacDonalds and the MacLeods in the 16th century led to the death of the islands entire population almost 400 in the Massacre Cave. The entrance to this cave is quite small and at one stage you have to crouch down very low for a short length. Once inside it is very large and we used flashes from our cameras to get some light. Needless to say we did not manage to get very far; a reminder to bring torches on our next visit for the cave is extensive and worth exploring. On the foreshore, at low tide there is a distinctive dyke containing tabular crystals of white feldspar up to 10cm long and 1.5cm across.
Cathedral Cave also necessitates a low tide for access which, of course, we had; excellent planning once again Angus. This cave has a very large entrance and is expansive inside but a torch, once again, is needed to explore more fully. Here lava geology was very interesting with a reddened lava flow top near the high-tide mark at the base of the cliff, amygdales (filled gas bubbles) and examples of pipe amygdales at the base of a flow.
Our last day but fortunately our ferry back to Arisaig was not to leave until 1700 hours giving us another day on the island. Great for once again the weather was perfect. As we walked along the track westwards towards the clearance villages there was a small exposure of basalt with spheroidal weathering also known as exfoliation or onion peeling. To give you an idea of the scale one member of the group remarked that the formation on the right looked like a birds nest.
We had more excellent views of An Sgurr, green hairstreak butterflies, stonechats, wheatears, willow warblers and magnificently whilst we were having lunch at Grulin Iochdrach a golden eagle appeared. Wonderful! This walk also took us past vast, cottage-sized boulders forming the Grulin landslide (or rock-fall).
A few of us decided that we would like to see the conglomerate at the termination of the pitchstone ridge at Bidein Boidheach. After crossing open moorland we were rewarded with fantastic views and though it was much too dangerous to get to the conglomerate we could clearly see the relationships between the basalt, conglomerate and the pitchstone. We found that the best route back was to keep to the path along the cliff top and after the burn strike out inland towards the grassy swards.
Our return journey was along the outward track and this gave us our last views of An Sgurr
Looking forward to my next trip to Eigg; still so much more geology to see! The perfect weekend did not conclude when we arrived at Arisaig for on the homeward drive we had the full moon, very low in the sky to accompany us.
For those of you who are interested in the wild flowers the following 32 species were seen though, no doubt, there were many that we missed:
Early Purple Orchid
I hope that my account of the weekend has been of interest to you and has whetted your appetite enough to encourage you to give your name to Angus for I am sure that he will be organising another Isle of Eigg excursion for next year. I would like to thank those on the trip for their companionship and many thanks to Karen for the evening meals that were absolutely delicious and without exception enjoyed by all.