Geology & Wildlife
Group Organiser: Jeremy Fenton
Phone: 01445 712663
U3A Geology and Wildlife Group 2017
I suggest that we continue the series of walks this year, but am open to other suggestions.
The third Thursday of each month from April (I’m away in Feb/Mar), meeting 11.00 at Achtercairn viewpoint unless arranged otherwise. Bring a picnic lunch.
The first three months are: April 20th, May 18th, June 15th.
I’ll email near the day when the likely weather is known, and say where I suggest that we walk (feel free to make proposals). Possibilities include: Rubha Reidh (if the road is open), Cave Hill and Old Wood (above Achtercairn), Flowerdale, Inverewe Estate, Heights of Kinlochewe (when hydro works are finished)... and repeats of walks which you missed.
Next Geology Meeting
The next walk is on Thursday 15th June, meeting 11.00am at Achtercairn Brae viewpoint car park as usual.
Venue to be decided (suggestions welcome!). Perhaps the “waterfall circuit” south of the Red Stable.
Reports from Previous Meetings 2017:
Thursday 18th May: Cliff Hill
7 present. A few light showers and a cool breeze did not stop us enjoying the walk from the Tollie car park up Croft Hill and then Cliff Hill on a generally fine day. A long list of plant species was identified, most abundant being lousewort and milkwort, with examples of butterwort, sundew, stonecrop, primrose, mountain everlasting, fir clubmoss, heath rush, common sedge, black bog-rush, purple moor grass, etc; but almost no animal life. The Lewisian Gneiss geology is particularly interesting here, with some very complex rock including meta-gabbro, early mafic bodies, a Scourie dyke, and intrusive pegmatite near the summit. The views down to Poolewe and along Loch Maree were very fine and also held considerable geological interest.
Thursday 20th April: Achtercairn
6 present. In a generally fine Spring we hit a poor day, and had to limit the wood+hill planned walk to the wood only. We walked through the upper part of the "Old Wood", the Victorian plantation SW of the Quarry, mostly larches and pines. A few spring flowers were emerging, but the main interest was mosses: we studied ten of the most common ones and tried to learn to identify them.
U3A Geology & Wildlife Group : 2016 programme
I propose that we re-start in March, normally meeting as before on the 3rd Thursday of each month at 12 noon meeting at the Achtercairn viewpoint (or elsewhere by arrangement).
Please tell me if you think this should be changed in any way, and also if you do not wish to continue in the group!
Normally all meetings will be outdoor walks, but if weather is foul on the day we could come indoors.
Possible places to visit:
Tollie path (Gneiss, antiform effects)
Heights of Kinlochewe path (Cambrian rocks, Moine Thrust)
Stattic Point (Torridonian, Stac Fada)
Rubha Reidh (Torridonian)
Red Barn/Stable and Old Road area (Loch Maree Group)
Flowerdale waterfall circuit (Loch Maree Group, Flowerdale fault)
... and repeats of last year’s walks for those who didn’t come
... and any other suggestions you may have
Other Useful Information
Pete Harrison from Ullapool and the Geopark is speaking on local geology (arranged by the Friends of Inverewe) on Wednesday 21st Sept, 7.00 at Inverewe Restaurant.
On Saturday 24th September, Channel 4’s programme “Walking Through Time” will feature the Stac Fada meteorite rock and the impact site at Lairg, which has recently hit the media.
Reports from Previous Meetings (2016)
Thursday 13th October: Beinn Eighe Mountain Trail plus
4 present. This was a much tougher walk than usual, and so numbers were small. We climbed the Mountain Trail by the down route, disturbing fieldfares in the wood; other wildlife included a stag with hinds, two froglets, long-tailed tits and a raven. Our main object was geological: a look at two little-known but outstanding areas of Mylonite. This is a metamorphic rock formed from local rock by the pressure and temperature of a Thrust, in this case the Moine Thrust which moved the top of Meall a' Ghiuthais into place. A long stretch of the path was on a greyish mylonite with small-scale foliation; often steps had been cut into it. The Torridonian sandstone next to it was very damaged, many cracks filled by veins of quartz. Higher up we left the path and wandered into a rarely visited but rather wonderful area to the north of Meall a' Ghiubhais, dotted with lochans. The wind was cold, but autumn colours were developing nicely including bright red mountain bearberry. We reached a small hill with a remarkable area of folded and contorted mylonite on its top: quite hard to explain! Then we circled the lovely Loch Bhanamhoir and headed back to the path and down the same way.
Thursday 15th September: Meall Aundrary
Most of this walk was off-path on rough or boggy ground (much enjoyed by our three dogs), although quad-bike tracks made by the tree-planters were often helpful. Yet again the weather was good, and even too hot until a breeze started. We walked from the Red Stable, first visiting the marble quarry just above where the 2 billion year old rock had been extracted for lime. The aim was to circle Meall Aundrary, a very craggy amphibolite hill. We looked out for evidence of the Creag Bhan Crush Belt where the Gneiss and the Loch Maree Group rocks had crashed together, and found damaged-looking gneiss and pseudotachylite (google it!). Little animal life was seen, but there was plenty of plant interest. We pondered the wisdom of planting 2 million trees in this area; there were some healthy patches, but over most of the landscape the vision of "dense woodland" had been totally unrealistic. We took a rarely travelled route round the end of the hill in fine rock scenery, with evidence of past shielings and walls perhaps made to keep cattle from straying, and finally managed to reach the Old Road. The remarkable Sulphide area (hot smokers) was studied; in the 1980s holes had been drilled here up to 600m deep to see if the deposits of iron, copper, zinc, silver and gold were worth exploiting (they weren't). We applied magnets to a boulder of Banded Iron Formation rock to prove the magnetite. And we finished at the shambles where a non-native spruce wood was recently removed, and where we had left a car.
Thursday 18th August 11.00
6 present. We set off from the big car park half way along Loch Maree and walked the shore as far as the River Grudie, in fine weather. In sandstone slabs bonsai-like trees of six species were growing in cracks, some with their feet in the water; small groves of pine managed on ledges sheltered from the wind. The heather was in full flower, and the bracken was turning to gold. Animal life ranged from frogs to an eagle (but with nothing in between). Our two dogs carried sticks and dug holes in sand and we wondered why. The geology, apart from the beautiful underfoot Torridonian, was mostly across the loch where most of the hills are made of Loch Maree Group rocks; we imagined the landscape without the Loch Maree Fault's movement, with Slioch near Kernsary. Lunch was on a sunny sandy beach. At the River Grudie we admired the two bridges and were horrified by the hydro-electric works: this bit of the National Scenic Area is very un-scenic at present. The half-overgrown old roads (Destitution 1849 and Military 1763) took us pleasantly back to the car park.
Thursday 21st July 11.00
8 present. The group name is now extended to "Geology and Wildlife", including study of plants and animals as well as rocks.
From Achtercairn viewpoint we wandered slowly up the hill Meall na h-Iolaire by the steep climbing path and down the easier way, stopping often to look at flowers, collect and identify grasses, examine the usefully coded backs of fern fronds, wait for a lost dog, etc. The geological interest was mostly in the view from the summit, the many erratics, and the signs of glaciation (the semipelite valley between amphibolite ridges, roche moutonnée, striations). It was a fine day, with a view as far as Foinaven. Perhaps the most exciting plant was a single Greater Butterfly Orchid, which last flowered on that spot six years ago. The spread of Northern Bedstraw up and down the path was noted, presumably carried on walkers' feet. A white Cross-leaved Heath was spotted. A rough count of plant species seen gives: 52 wildflowers, 9 grasses (recognised), 6 sedges, 6 ferns. Animals included ravens, some obscure flies, a Meadow Brown butterfly, fast-flying dragonflies, and a froglet.
Thursday 9th June 11.00
Only 3 managed the recent walk (I’m sorry about the change of date), which took place in perfect walking weather.A small party walked the start of the Tollie-Slattadale path, noting the damaged gneiss in places and some possible mylonite here and there, connected with the creation of the Tollie Antiform. We also looked at samples of cataclasite, although we didn’t see any on site. Then we examined two outcrops beside the path which contain pseudotachylite, a glassy black rock; dated 1000 million years ago, this was formed by an unknown episode of very violent movement and friction which melted the rock, at about the time when the Torridon Sandstone started to be laid down. Samples were taken here recently to help with studies on the possibility of life on Mars! We then turned right into the Antiform and aimed for a group of lochans before taking to a beautifully rocky ridge with all sorts of gneiss, including very deformed Scourie Dykes. It was a lovely walk on a day of perfect weather.
Try googling these three rocks!
Thursday 14th April.
9 present. We again had fine weather for a slow 7-hour circuit from Mungasdale. We followed the fine rocky shore to Stattic Point (Stoer Group Torridonian Sandstone), spotting on the way a Sea Eagle, a Great Northern Diver, and two puzzling boulders which looked like Ialltaig Gneiss from Gairloch and Moine Schist from inland. Our main target was the fine exposure of Stac Fada rock just before the point; we stopped here to discuss its origin in the cataclysmic collision, 1178 million years ago, of a 2.5km-diameter meteorite which is now thought to have landed near Lairg. Then we climbed the two small sandstone hills inland from the point. The second, Carn Dearg na h-Uamha (Red Cave Hill), is remarkable for a long overhanging cliff of "autoclastic" sandstone breccia (containing boulders made of itself, Diabaig Formation) which lies on a slabby base of much older Stoer Group rock. We returned via small hills of Lewisian Gneiss.
Two relevant resources:
This download is a technical but moderately accessible article about the Stac Fada rock with a new theory about the crater: well worth struggling through!
Googling the “cave” hill (Carn Dearg na h-Uamha) takes you to part of Stewart’s book on the Torridonian.
Thursday 17th March 12.00
8 present. Our first meeting of the year started with revision of rock types in Ardmor garden and the wall of Roundhouse 8 nearby. We then transferred to the Crasg viewpoint where we scrambled down to examine the extraordinary breccia below (Torridonian, Diabaig formation) and to enjoy lunch under a cloudless sky (yes really). From there we went to Flowerdale, and walked to the BIF rock (Banded Iron Formation) which magnets helped us to find: the only example of this rock in the UK. Beyond it we found the small marble quarry, with a little poor quality marble visible. Both these rocks are 2 billion years old, from a time when the living creatures needed to form them were bacteria.
The next walk will be on Thursday 14th April; if the weather permits, we'll walk to Stattic Point.
Reports from Previous Meetings (2015):
Thursday 19th November
The forecast said heavy showers or rain, and so it was dry most of the day. Having done a road trip south last month, we now set off northwards, stopping briefly at the Tournaig and Aultbea view-points to discuss the geology in the views; the Torridons were invisible, but Isle Ewe clearly showed off its distinct Torridonian and Triassic Sandstone parts. The Jurassic Limestone hereabouts is buried, only showing in the green of the fields. The next stop was at the former viewpoint (overdue for reinstatement?) before Laide Woods, on the obvious bouldery moraines of the Wester Ross Readvance, the point which the ice reached about 16,000 years ago.
A longer stop was made on the coast east of Laide, where we walked down to the Church Cave and the complex of sea stacks there, made of the youngest Torridonian Sandstone, the Aultbea Formation. The tide was high and waves were breaking in the little bays as we examined beautiful water-smoothed rocks and pebbles. Then we drove on to the top of Gruinard Hill where we lunched and puzzled over the Gneiss exposed in the road cutting, a complex mixture of pale and dark rocks.
Our last visit was to Laide beach. We walked or stumbled along the bouldery shore past strange smooth slabs of Triassic Sandstone, and breccia and conglomerate beds, as far as the waterfall and cave. Again, the rocks and pebbles were fascinating, beautiful and sometimes inexplicable. As we returned along the beach, a brilliant rainbow heralded the first rain of the day.
PS Many thanks to those who contributed to a generous gift which is enabling me to order a copy of “The Later Proterozoic Torridonian Rocks of Scotland: their Sedimentology, Geochemistry and Origin “ (!) by A.D.Stewart, the standard monograph on the TS. Hopefully I may be able in due course to pass on some of the more comprehensible parts of this for the benefit of the group!
PPS To find out about the exciting discovery of Reidite in the Stac Fada (meteorite) rock, google “Stac Fada Reidite”.
Thursday 15th October
7 present. On a fine day we were fortunate to spend the day in fine scenery beside Loch Maree. We met at Flowerdale to share cars. The first stop (after a geological tour along the A832) was the wonderful field of Torridonian boulders visible from the road 2km beyond Talladale. We found the easiest route to them, picnicked on one of them, discussed how they got there, and contemplated the Loch Maree Fault. Then we drove on to the Glas Leitir car park and studied Slioch's foundations: mostly amphibolite, and a famous "fossilised landscape". The bedrock here gave our first meeting with Cambrian Quartzite. The last stop was at the NNR Visitor Centre, impressively refurbished. We walked the mile-long Buzzard Trail, with stops to discuss the Moine Thrust. On Beinn a' Mhuinidh opposite its effects were clear: the thrusts resulted in a virtually upside-down hill. We could see the Moine Schist beyond Kinlochewe.
Thursday 17th September
8 present. Given the fluctuation in the number of those who could attend the first six meetings (from 4 to 17), and therefore the difficulty of running a systematic course, we have decided to concentrate on study visits to interesting places, only coming indoors in foul weather. This time we climbed Croft/Cliff Hill from the road, stopping to ponder every rock. There were Torridonian erratics, but the bedrock was Lewisian Gneiss, and there was a lot of it to be seen. We puzzled over the varied textures and colours (Scourie Dyke, Hornblende Gneiss, Early Mafic Bodies etc), pondered the foliation, patterns and folds (metamorphic effects), admired the large-crystalled pegmatite next to the wireless mast, and noted the Loch Maree Fault and the Tollie Antiform. The weather was kind (in spite of heavy rain in the forecast), and there were fine views.
Thursday 9th July
Not many were available, so there was no new geology; instead we set out to visit a few local sites. (1) The east end of the Old Road to Flowerdale, using a convenient new forestry track for access; we looked at a Banded Iron Formation boulder (magnetite), and the colourful and fascinating Sulphide Deposits. (2) Semipelite at the roadside near the Bad an Sgalaig dam. (3) A small Dolomitic Marble quarry above the Red Barn. (4) The Ard Gneiss / Sandstone unconformity at Shieldaig. We discovered that bracken is not good for geology.
Thursday 11th June
Torridonian Sandstone. We met out of doors and looked at some samples, noting the variety of textures from Breccia to Shale (or Siltstone). The sediments were turned to rock by the process called Lithification (squeezing out air, adding quartz cement precipitated from water); this is part of the process called Diagenesis which may also cause later effects on the rocks such as quartz veins or re-crystallising. Torridonian is laid down in beds or strata, but is also often very Jointed (joints, jointing); i.e. broken into blocks by vertical cracks, which help to explain the shape of the hills – terraces and small cliffs. The joints were mostly created as the weight of rock above was removed by erosion, and expanded by ice.
Words learnt: Breccia, Conglomerate, Shale, Lithification, Diagenesis, Jointing.
We then walked along the crags north of the Poolewe road and admired the many varied layers of breccia and sandstone in one formation: the Diabaig Formation, oldest (basal) layers of the Torridon Group, labelled TCD1 on maps.
Thursday 14th May, 2.00.
10 present (including two guests).
Loch Maree Group: a complicated but very special local set of six rocks, 2 billion years old.
We viewed samples, and looked at where the rocks are found and how they were formed.
Words learnt: Subduction, Accretion, Collision; Hornblende; Biogenic, Intrude/Intrusion
We drove to the Golf Club car park and walked a short Flowerdale circuit, noting the effetcts of the Flowerdale Fault. We diverted to look at two Biogenic rocks: Banded Iron Formation (BIF), using magnets to test for it with great success; and the nearby marble quarry where we wondered which rock was the marble. We then walked the Harbour-Beach path and studied the Ard Gneiss which was intruded into the LMG and is notable for the Augen ("eyes" of feldspar) seen in much of it.
Thursday 9th April 2.00
17 present (including two guests).
It was a fine day for a 2-hour walk with a large party exploring Lewisian Gneiss in the area north of the Gairloch-Poolewe road. We discovered that it is a very varied and complex rock with notable intrusions, especially the many Scourie Dykes and a few examples of Pegmatite. Other features of interest included very thin foliation, many areas of small-scale folding, and quartz veins of all sizes. We finished by looking at outcrops of Torridonian breccia (Diabaig formation), which included broken pieces of the gneiss.
Thursday 5th March 2.00
Lewisian Gneiss: view samples, talk through history, slide show; issue new guide book “Wester Ross Rocks”.
Words learnt: Protolith, Quartz, Feldspar, Dyke, Felsic, Mafic.
No walk: poor weather!
Thursday 5th February 2.00
Introduction to the Big Four local rocks: Gneiss, Amphibolite, Sandstone, Quartzite; study sample rocks; slide show on Scotland and its landscapes.
Words learnt: Igneous, Metamorphic, Sedimentary; Crystalline, Clastic; Foliation, Bedding.
Walk to roundhouses to look at stones and up hill path for the view and to collect samples.
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