Malvern U3A Geology Group

The Drumadoon Sill near Blackwaterfoot, Arran

Field Trip to Arran

22-27 September 2019

Itinerary and Notes on the Geology of Localities to be visited

Introduction (Text extracted from an article written by Stuart Blake – our guide on Arran) Arran - Scotland in miniature; the island where every view reflects varied geology and you can literally ‘walk through time’ across the landscapes The Isle of Arran, well known for its varied scenery, sits astride the Highland Boundary Fault and is therefore an excellent place to appreciate the variety of ‘Highland’ and ‘Lowland’ geology that Scotland is famous for. That’s why so many geology students go there! There are not many places on this planet where, in a three- kilometre walk, you can see evidence of changing environments that span more than 100 million years from Devonian to Permian times. The sedimentary rocks of Arran’s east coast record Scotland’s journey across the Equator, from desert conditions, through the Equatorial swamps and back to desert again. You can literally become a time traveller, passing through the multiple environments and climates Scotland has experienced over millions of years. You can see conglomerate and sandstone deposited on land in braided stream channels during seasonal floods, followed by alternating layers of limestone, coal, sandstone and mudstone formed at the Equator, and then pass into Permian desert sandstone with dune bedding and wadi-type breccia deposits – a truly amazing assortment of geology. In the 1780s, James Hutton visited the north of Arran and discovered the junction between these sedimentary rocks and the underlying, even older, eroded metamorphic rocks of the Highlands. This was one of his first ‘unconformities’, which he used to demonstrate the great age of the Earth and the evidence of ‘former worlds’ where different rocks had been formed by natural processes. As if this was not enough, Arran has many other must- see sites that include a giant myriapod trail, Arthropleura, filmed by Sir David Attenborough in “Life on Earth”, one of the oldest tracks of any land creature. Early reptiles, including a crocodile-like reptile, left Chirotherium prints in Triassic sandstone layers of the south of Arran. The interior of north Arran is dominated by a ten- kilometre-wide granite pluton formed by magma intrusion 60 million years ago, at the time the Atlantic

Ocean was starting to form. This mass of tough igneous rock was in turn dissected by dykes and then eroded by glaciers, forming the majestic and very jagged skyline of today. In the south, at around the same time as the Northern Granite was forming, there was a more varied and smaller-scale intrusion of magma that has resulted in a range of interesting coastal features. The Doon cliff at Drumadoon is a tremendous example of an intrusive sill that has resulted in a very imposing headland of 30-metre high columns. Close study of this headland tells the story of changing magma composition over the formation of several intrusions. Equally impressive are the sills and raised beaches of Holy Island and Pladda.

The Stratigraphy of Arran Finally, recent settlers have left their mark on Arran by taking advantage of the raw materials and structures. Sea caves on the raised beach were used as seasonal dwellings, sandstone used for standing stones and igneous pitchstone shaped into axe heads and cutting blades. More recently limestone was processed in limekilns to improve the fields, and barytes was mined from veins.

A Simplified Geological Map of Arran

A Road Map of Arran

Itinerary and Notes on the Geology of Localities to be visited

Sunday 22nd Sept Time Action 1400 Depart Malvern and drive to North Lakes Hotel & Spa, Penrith 1900 Check-in North Lakes Hotel & Spa, Penrith (Approx. 5 hours with stops) Monday 23rd Sept Low Tide 1247 Action 0900 Depart Penrith Hotel and drive 2 hrs 45 mins to Ardrossan 1145 Arrive Ardrossan Ferry port Low Tide: 1247 1230 Depart Ardrossan on CalMac Ferry (Option A - Lunch on Ferry) High Tide: 1846 1330 Arrive Brodick (Option B - Lunch in Brodick) 1430 Arrive Best Western Kinloch Hotel, Blackwaterfoot In the afternoon, a short walk to examine the Blackwaterfoot to Tormore coast using the GGS Guide - Drumadoon Sill and Judd's composite dykes. Bus to Tormore and walk back to Hotel at Blackwaterfoot (6.3 km, 100m 1500 ascent) If weather is poor we will walk from the hotel and assess how much of the

walk it is worth completing. The text below is taken from a publication of the Geological Society of Glasgow: Excursion Itineraries, Isle of Arran, DRUMADOON AND THE TORMORE DYKES, Version 1.0, by J.G. MacDonald.

Drumadoon and the Tormore Dykes The object of this excursion is the examination of the composite dykes and other intrusions which abound on this stretch of shore. It can be carried out by public transport from the main centres on the east side of the island. If private transport is used it will be found more convenient to arrange for collection at the appropriate terminal point, especially if another excursion is to be made on the same day. The Tormore shore is reached by the track that leads westward from the main road at the old post office [Grid Ref. NR 8950 3245]. The route follows the raised beach southwards past the houses. As an alternative, for those who wish to restrict their visit to an examination Judd’s dykes, and the localities between King’s Cave and Cleiteadh nan Sgarbh, cars can be left at the car park beside the Blackwaterfoot to Machrie road (A841) on the east side of the forestry plantation [NR 8981 3148]. A path skirting the plantation on its north side leads to the shore close to An Cumhann (locality 3). Another path through the plantation reaches the shore at locality 5, south of King’s Cave. 1. The Tormore Shore. The foreshore and raised beach cliff are eroded in sandstones attributed to the Lamlash Beds in the upper part of the Permian succession of Arran. These sandstones are often strongly cross- laminated and carious weathering is locally striking. Irregular distribution of carbonate cementing material leads to hard, rough-weathering bands alternating with soft red sandstones and siltstones. Pseudomorphs after halite and dendritic gypsum are recognisable in places. 2. Judd’s Dykes. Along this stretch of shore numerous dykes crop out including the composite dykes made famous by Judd (1893). The finer points of the petrography of these interesting intrusions must be studied in the laboratory but the constituent rock types are sufficiently diverse to enable adequate field determinations to be made. These types include felsite, quartz-feldspar-porphyry (quartz- porphyry of the 1:50 000 BGS map), pitchstone, and dolerite. The Roman numerals used by Judd

5 to identify the dykes that he described are appended in Figure 1. The most northerly pitchstone was not considered to be composite by Judd but it encloses some areas of felsite; it forms a conspicuous feature on the foreshore, about 5 m thick at high water mark but is variable in thickness and dip. The intrusion trends ENE–WSW and is composed mainly of dark-green pitchstone.

Judd’s dyke No I. This N–S trending, dark green pitchstone dyke crops out south of the most northerly pitchstone but the relationship of the two is unclear. It is about 4.5 m thick. It disappears beneath boulders and raised beach sediments but reappears south of dyke III where it dips to the east. Southwards its trend swings towards the SSW and the dip gradually decreases. By the development of felsic modifications and the presence of thin, generally rotted marginal tholeiite the intrusion becomes composite. Flow-banding is strikingly displayed, especially in dislodged blocks on the shore.

Judd’s dyke No. II. A central 4.5m thick, east–west trending, quartz-felsite is bounded by sphereoidally-weathering tholeiites 1.2m and 1.8 m thick on the north and south margins respectively. Judd records the felsites passing in places into “pitchstone-porphyry or ’vitrophyric’ rock” which is stated to occur “as a band varying in width from 150 to 600 mm, sometimes forming part of the quartz-felsite mass and at other time intersecting the masses of andesite” (i.e. tholeiite). Some 55 m S of dyke II, two dykes intersect; they have irregular trends that diverge as they head for the raised beach cliff. Judd’s dyke No. III. This NW–SE trending dyke consists of pitchstone, 1.2–1.8m thick, with an olivine-dolerite on its north side. The dolerite differs in composition from the tholeiites usually found in association with the pitchstone and felsites of the composite intrusions, so Judd No. III might not be composite in the normal sense but the result of the fortuitous intrusions of two totally unrelated magmas. Judd No 1 reappears just south of this. 3. An Cumhann. Judd’s dyke No IV, a 27m wide composite dyke, completes forms a prominent feature that stands high above the shore line and blocks the passage along the beach platform except at low tide. Otherwise it can be crossed by ascending a poorly defined path over the top on the shoreward side. The bulk of the dyke is composed of quartz-feldspar-porphyry with abundant large phenocrysts of white-weathering orthoclase feldspar and smaller glassy ones of quartz set in an aphanitic grey groundmass. The marginal tholeiites on both sides, although basaltic in composition, contain scattered xenocrysts of orthoclase similar in appearance to those in the centre of the intrusion. 4. King’s Cave. South of An Cumhann the cliff at the head of the raised beach rises to a greater height. It has been hollowed out by wave action when sea level stood higher during early Post-Glacial times. The largest cave, known as King’s Cave (Fig. 2) is entered by a gate in an iron railing. The gate is normally left open. It gets its name from the legend that King Robert the Bruce hid in it when he was in Arran. There is historical evidence that he passed through Arran on his journey from the Island of Rathlin to Ayrshire in 1307, but no written record exists of his visiting this site. The cave was formed by the erosion of two upwardly converging joints in the Permian sandstone. When wave action undermined the cliff the unsupported rock between the joints collapsed and the resulting debris was washed away. Little of archaeological significance has been found here. Fig. 2 King’s Cave. The figure is ~1.6 m high 5. Signpost for Blackwaterfoot. A short distance south of King’s Cave, at a recess in the cliff, a short climb leads to a branch in the path. A signpost indicates the route south towards Blackwaterfoot and the path to the King’s Cave car park. The view of the north side of the recess (Fig. 3) shows sandstones intruded by a thick felsite sill, mostly deeply weathered to red and yellow ‘sandy’ material. Above the sill there are more sedimentary rocks capped by a sill of pitchstone. Pitchstone crops out at several points in the recess and most readily at the base of the conspicuous knoll on its south side. Partially devitrified pitchstone occurs in a low cliff below the footpath.

Fig. 3 View north from the path to King’s Cave car park. Felsite and pitch-stone sills are intruded into sandstones of the Permian Lamlash Beds - a short distance south of King’s Cave. The above recess has been considered to mark the line of a NW–SE running fault coinciding with the junction of the Permian Lamlash Beds to the north with the Triassic Auchenhew Beds to the south (Tomkeief 1961). It is certainly clear that there is a change in lithology; the sedimentary rocks to the south are finer grained with a high proportion of marls. The path continues along the raised beach for about 800m towards Cleiteadh nan Sgarbh. Auchenhew Beds crop out sporadically along the shore. 6. Cleiteadh nan Sgarbh. The promontory here is formed by a NNW-trending composite dyke complex, similar in some respects to An Cumhann (locality 3). The widest member is quartz-feldspar porphyry 15.5 m thick flanked on either side by ~0.6 m thick basaltic intrusions (Fig. 4). The quartz-feldspar porphyry is darkened at its margins and the marginal basalts contain xenocrysts of orthoclase feldspar, similar to, but less abundant than those in the porphyry. On the east side a 9 m thick felsite dyke is in contact with the eastern marginal basalt. The felsite is flow banded parallel to its western side and has weathered to shades of bright-red and yellow which make it look deceptively like sandstone in places. The intrusive complex is inclined to the east and at the top of the beach its heading changes towards the southeast as it crosses the raised beach. It crops out in the cliff to the north (to the left) of the Drumadoon sill.

Fig. 4 View from Cleiteadh nan Sgarbh towards the Drumadoon Sill. Note the annotation on Fig. 4: A – felsite; B – quartz-feldspar porphyry

7. Drumadoon. (See photograph on the Title Page) Follow the track from locality 6 from the foot of the raised beach cliff up the slope to the north end of the Drumadoon Sill. Then continue along the top of the talus slope where marly sedimentary rocks below the sill can be examined as can the basal rocks of the intrusion. At the base of the sill is a sheet of tholeiite, about 1.2 m in thickness thinning to about 0.8m at the south end of the cliff. Above that rises the main quartz-feldspar porphyry with its columnar jointing which has inspired the local name ‘Organ Rock’. Near its base the porphyry is darkened and is rich in xenoliths of tholeiite which have a tendency to weather out. Fallen blocks of xenolithic porphyry litter the talus slope and the adjacent shore. Fragments of a thin upper marginal tholeiite have been reported (Tyrell 1928, 200) supporting the view that the Drumadoon sill was intruded during the same episode as the composite dykes. [Research carried out since the publication of the 1983 edition of the Macgregor Guide (Meade et al. 2009) throws new light on the nature and of the Arran composite intrusions.] 8. Drumadoon Point West of the Drumadoon the composite sill steps down to shore level, possibly as the effect of an EW oriented fault. The same relationships between the main quartz-feldspar-porphyry and the margin tholeiite occur here and at Drumadoon Point the eastern margin of the intrusion can be examined. At the Point the marginal tholeiite dips to the east. Note also the presence of an igneous breccia with a matrix of yellowish porphyry, a thin composite dyke and a number of basaltic dykes that cut the main sill. 9. Composite dyke Here a NNE-trending quartz-feldspar-porphyry dyke with a darkened eastern margin cuts the shoreline. Its projected line runs to the north of the eastern margin of Drumadoon suggesting that it may have been the feeder to the sill. It resembles the dyke at Cleiteadh nan Sgarbh (locality 6) and that at An Cumhann (locality 3). This raises the possibility that all three dykes and the Drumadoon sill are connected and were intruded at the same time. This locality is situated close to the north-western end of Blackwaterfoot Golf Course which is laid out on coastal sand dunes. Care should be taken to keep clear of fairways and maintain a good lookout for unexpected wayward golf balls whizzing towards you. 10. Blackwaterfoot The beach margining the golf course is cut in several places by basic dykes. On the shore, south of the Golf Club House, the dip of the country rock marls and sandstones increases to about 50° against the Blackwaterfoot–Torr Righ Mor felsite. At the contact the felsite is flow banded; east of this flat lying joints give a roughly ‘stratified’ and, in places, a rippled appearance. Elsewhere columnar joints are well developed, as seen at the Blackwater Bridge beside the harbour. Dykes which trend in the same direction as the felsites have irregular courses, “as though they were influenced by the proximity of the felsites or found it difficult to penetrate it.” South of the Club House the remains of two sea-stacks stand in front of the raised beach sea cliff. Farther to the SE the cliff shows a patch of the Auchenhew Beds, with columnar felsites to the west. Felsite on its E side has joints disposed in an asymmetric arch; this feature was noted and figured by Bryce (1872). The stacks and arch are situated in private grounds.

Coastal route from Kinloch Hotel, Blackwaterfoot to Tormore.

Terrain: a rough path and sections on boulders requiring good walking boots. Wear appropriate clothing for inclement weather. Nearest toilet facilities are at the Kinloch hotel. 1730 Arrive back at Hotel 1830 Dinner

Tuesday 24th Sept Low Tide 1420 Action Depart Hotel by coach and drive to 500m north of Derenenach on the 0900 Low Tide: 1420 Blackwaterfoot - Brodick road. Tide state not Objective - Study the easily accessible parts of the Central Ring Complex important in AM 0930 Arrive Derenenach (NR 930337) In the morning, visit a number of localities on the margin of and within the Central Ring Complex - Part of Excursion 5 in the GA Guide Locality Brief Description of Localities In the quarry next to the Allt nan Dris burn we will examine the fine-grained granite with orthoclase, plagioclase, quartz and lesser hornblende and biotite. This granite is fairly typical of the several granites which are the most abundant rock-types of the 1 Central Ring Complex. Walk up the north bank of the Allt nan Dris and take the central of three burns in the hillside. NB: Quarry seems to have been expanded recently Red, probably Triassic, siltstones outcrop in the stream bed of the southern tributary 2 of the Allt nan Dris. Thin limestones and black shales outcrop in a small gorge further upstream. Rare 3 samples of Rhaetavicula contorta are found - a Rhaetian bivalve. Return to the bus and drive to the lay-by opposite Glenloig Farm (NR 946351). Cross the bridge and immediately turn left (south) through the first gate and follow 4 the path up the hill. Examine boulders of rhyolitic (felsic) agglomerate with a variety of clasts set in a fine-grained, acid groundmass. See Locality 6 below Carry on up the hill to a small disused quarry on the right of a conspicuous hollow with grassy slopes near the skyline with exposures of a white calcareous rock below and basalt above. The calcareous rock has yielded Cretaceous fossils and the succession appears identical to that in Antrim, N. Ireland where Cretaceous chalk is overlain by Early Tertiary flood basalts. The chalk shows contact metamorphism. 5 On the east side, adjacent to vent agglomerates there is a narrow zone of skarn minerals - pale yellow andradite-grossular garnets with magnetite, clinopyroxene and epidote. When the chalk was laid down Arran was below sea-level. Uplift preceded the Palaeocene and the Chalk cover was eroded away leaving only remnants. Palaeocene basalt lava flows were erupted sub-aerially preserving some of the remnant Chalk. To the east of the quarry, excellent exposures of rhyolitic agglomerates are seen in the NW-facing cliffs. Clasts of quartzite, vein-quartz, Dalradian schist, ORS sandstone, 6 basalt, felsite, porphyry and granite. Many clasts are well-rounded - some of the older rocks may have been rounded in old ORS rivers but the younger rocks were rounded by erosion during emplacement of the Central Ring Complex. Return to the bus and drive eastwards to NR 969354 (NR 969354) A small unpromising exposure of loose rocks immediately east of the bridge and south of the road shows good examples of hybrid diorites. Pre-existing gabbros have been invaded by granitic magmas and partially converted to 7 intermediate rock-types. Various stages of this can be seen at this locality. Darker rocks are still relatively basic whereas lighter coloured rocks have suffered more extensive hybridisation; veins and patches of pink and white material represent the acid magmas responsible for the hybridisation. 1245 Drive to Brodick 1300 - 1415 Lunch in Brodick

Maps of the Central Complex Walks (from GA Guide to Arran)

Dr Bob Gooday led the group round the Central Igneous Complex. Handout Extract from his PhD

BGS map of the Central Complex

OS Map (not to scale) of the Central Complex area

In the afternoon, drive to Clach a'Chait, north of Corrie, and follow the Glasgow Geological Society Guide - Corrie Shore. 1415 Drive to Clach a'Chait, north of Corrie Low Tide: 1420 1430 Walk south from Clach a'Chait on Corrie shore to locality 14 (GA & GGS Guides) High Tide: 2018 The walk must be undertaken at low tide in the afternoon.

Wear appropriate clothing for inclement weather. Nearest toilet facilities are at the Corrie Hotel and various tearooms 1730 Arrive back at Hotel 1830 Dinner

The geology of Corrie Shore is covered in good detail in the Geological Society of Glasgow Excursion Itineraries, Isle of Arran, CORRIE SHORE, Version 1.1 by J. G. MacDonald from which the following text has been extracted. It is also described in Geologists' Association Guide No 32 Isle of Arran - WS McKerrow and F.B. Atkins as part of Excursion 2.

Wednesday 25th September 2019 0900 Leave Hotel and drive to Sannox Bay (16 miles; 30 minutes) Low Tide 1534 0930 Arrive Sannox Bay In the morning, examine Localities 16 to 24 in Glen Sannox - Excursion 2 of the GA Guide Locality Brief Description At Sannox Bay, note the following geomorphological features: the spit created by southerly long- 16 shore drift; raised beaches and river terraces The Glen Sannox Baryte Mine: Baryte (BaSO4) occurs as veins within fine-grained Lower ORS sandstones and coarse, quartz-clast conglomerates. Sediments dip 200 to 450 to the east and the veins (6 in total) strike N-S across the valley and hade/dip to the west, varying in thickness from 2 m at surface to 8 m at 30 m depth. The barytes is coarse-grained in places and the veins are 17 virtually mono-minerallic with only occasional hematite, epidote, calcite and dolomite and very occasional malachite. Slickensides, pinching and swelling and occasional xenoliths point to emplacement in faults and fissures which were active as the veins were being formed. Dunham (1952) proposed they were of Hercynian age. (NS 006456) Anastomosing veins on S side of the Sannox Water. Also, a dump from which samples 18 can be collected. Conglomerates forming crags higher up the hillside are typical of Lower ORS. The development of epidote and chlorite around the larger clasts may be due to thermal metamorphism associated 19 with the Northern Granite. (NS 003457) Some 150 m to the west, a larger crag permits an estimation of the direction of flow 20 of an early Devonian River (Hint: imbrication) (NR 992468) Examine Dalradian turbidites in the river bank above the bridge. These strike across the river and dip steeply. Check graded bedding to see if the rocks are overturned. The rocks were 21 originally deposited as greywackes from turbidity currents; subsequently metamorphosed to 0 greenschist facies - less than 400 C and 5 kilo bars pressure. (NR 995469) Lavas, exposed along the river, have pillow structures with the concave surfaces of individual pillows generally facing downstream. The pillow lavas represent submarine eruptions of basaltic rocks, now altered to spilite by the conversion of labradorite plagioclase felspar to albite 22 and of pyroxene to chlorite. The outer zones of the pillows, once glassy, have now devitrified but zoning can still be seen. (NR 995469) The pillow lavas are succeeded in turn by a thin agglomerate and black, pyritic shales 23 - dipping and younging to the east. The lavas have been dated as Ordovician. (NS 980474) Note the finer-grained chilled margin of the Northern Granite (up to 1 m wide) with occasional quartz-rich pods up to 3 m beyond the granite. Note also thermal metamorphism of the Dalradian within 0.5 m of the granite margin. The northern Granite is characterised by: a very narrow chilled margin; a very narrow thermal aureole; few if any quartz apophyses in the country 24 rock; few if any xenoliths near the margin and up-doming of the country rock. Consequently, it is thought the last stages of emplacement were by the ballooning-up of a crystal mush (NB: Nigel Woodcock’s lecture to Malvern U3A Geology on the intrusion of the Shap granite and Prof. Cathie Cashman’s lecture on “What lies underneath a volcano”). 1245 Depart Glen Sannox by coach and drive to Lochranza for lunch

In the afternoon, a walk to Hutton's Unconformity and round to the North Coast using the GGS Guide 1400 Depart Lochranza by bus for road across Glen Chalmadale towards Lodge Farm The geology of the North Coast is covered in good detail in the Geological Society of Glasgow Excursion Itineraries, Isle of Arran, Loch Ranza, North Newton and the Cock of Arran, Version 1.0 by J. G. MacDonald, from which the following text has Low Tide: been extracted. 1534

Terrain: Roadside exposures, footpath and sections of beach with boulders requiring good walking boots.

The distance walked is optional; people may return to Lochranza as they wish. The route is clear and easy to follow as long as you return to the bus for a 1630 departure.

Wear appropriate clothing for inclement weather.

Nearest toilet facilities are at the Lochranza Centre in Lochranza 1630 Depart Lochranza 1700 Arrive Hotel 1830 Dinner

Thursday 26th September 2019 0900 Leave Hotel and drive to Catacol - 16 miles, 30 minutes Low Tide 0930 1634 Arrive Catacol In the morning, examine the contact between the Northern Granite and Dalradian schists using the GA Guide from which the following descriptions of the localities have been extracted. Note: The weather in Arran recently has been very wet and flooding has been widespread. Parts of the itinerary below may not be accessible. If so, we may visit an area of similar geology in Upper Glen Sannox. Locality Brief Description (NR 911487) The black graphitic shales exposed in the burn are Dalradian and dip 700 to the NW - 1 away from the N. Granite. This is probably a hiatus in turbidite deposition. (NR 913486) Climb to the conspicuous crag of Dalradian schists above the hut and observe various geomorphological features. Further upslope there is the chilled margin of the granite, fine-grained 2 veins and irregular off-shoots of granite penetrating Dalradian and blocks of Dalradian completely engulfed by granite. (NR 913483) The granite/schist contact, which is highly irregular in outline with intercalations of 3 granite and schist - suggestive of some stoping. (NR 911482) A moderately coarse-grained diorite dyke intruding the schists but not the granite which it pre-dates. Dark hornblende, biotite and andesine plagioclase. Age is unknown. Unlike Central 4 Complex diorites – there is no evidence of hybridised gabbro; it appears to have crystallised directly from a magma of intermediate composition. Note veins and irregular offshoots of granite nearby. (NR 909482) Along the line of a small cliff to the NE of the burn, occasional patches of brecciated and 5 re-cemented Dalradian schist are interpreted (Harland 1987) as infillings in fissures in the old land surface that became the Caledonian Unconformity. (NR 903488) (Near the road but further south) Good example of asymmetric drag folding in Dalradian 6 schists with graded bedding. Drive to Imachar, park in parking place and walk north to a vertical, Carboniferous (?) quartz-dolerite 7 dyke on the shore and in old quarries nearby. Pink, felspar-rich veins have a high potassium content, not explainable in terms of simple differentiation - possible remobilised Dalradian? 8 At Machrie (NR 889351) unconformable Upper ORS and Permian contact (when tide is low) 1230 Drive to Blackwaterfoot for lunch or on to Levencorroch for a picnic lunch.

Map of localities 1-6 in the Catacol area

OS Map (not to scale) of the Catacol area

In the afternoon, drive to Levencorroch on the south coast for part of Excursion 6 in the GA Guide Brief Description (NS 011219) Levencorroch At the flat area where the burn emerges from a narrow gorge look upwards east and west at a thick Tertiary quartz-dolerite sill. Fallen boulders provide good specimens. The gorge may follow a Tertiary or post-Tertiary fault. On the west side of the gorge, about 40 m downstream, a dolerite dyke runs parallel to the valley with sandstones to the west and 1 shales and sandstones to the east. A second dyke shows excellent spheroidal weathering. The sediments below the waterfall are the Triassic Auchenhew Beds - note the parallel bedding and the dominance of clays and fine sands. Marked contrast to the fluviatile, flash flood and wind-blown Permian sediments. However the absence of marine fossils suggests a non-marine environment - possible lake deposits, the presence of desiccation cracks indicating them as impersistent. Fifty metres above the waterfall a dolerite dyke shows variable amounts of plagioclase crystals. It splits into three parts the left of which can be traced as far as the waterfall where its attitude changes to the horizontal and it is displaced by a small fault, terminating upwards in a shallow dome. 2 The right hand extension becomes attenuated above a sandstone bed. It is unusual to see the termination of a dyke and it is worth examining this locality. Low magma pressure is indicated by the sinuous shape of the intrusion and the way it is affected by lithological changes in the country rock. Thermal metamorphism is neglible. The sediments themselves show occasional ripple marks and mud cracks. A fossil footprint collected from here is in the Oxford University Museum. The sandstones are rich in muscovite and some show trough cross-bedding. ALLOW 90 MINUTES FOR LEVENCORROCH Drive on to (NS 022210) and park in lay-by next to a thick olivine analcite dyke (crinanite) forming a prominent feature on the shore. Near its SW margin the dyke shows a very coarse-grained, slaggy zone with vesicles infilled with the zeolite thomsonite. It also contains rare xenoliths of leucocratic (pale) crinanite. The regional dip of the Triassic sediments is general 50. However next to the dyke they dip at up to 400 away from the intrusion on its south-west margin, indicating an upward motion of the intrusive 3 magma. Isolated outcrops of mudstones and siltstones on the beach show desiccation cracks and adhesion ripples. Adhesion ripples are irregular, parallel crests of sand formed when a wind blows dry sand across a smooth moist surface. In cross-section they are asymmetric with the up-wind slopes steeper than the lee slopes. Drive east along the shore road and park on the verge by a bend to the left. At (NS 034208) descend the first flight of steps nearest the road and study the vesicles in the vertical face of a felsite sill, exposed at the western side of a broad grassy platform. Most of the vesicles have 4 flattened bases and convex tops. Harland (1987) suggested the lithostatic pressure was relatively low and that the sill was intruded within 200 m of the surface. Drive to Dippen and park in the lay-by. (NS 050229) A small quarry to the west of the lay-by exposes the Dippin Sill – a large crinanite (an analcite olivine dolerite emplaced in Triassic sediments. Note: coarse grain size and patches of white 5 analcite. A younger dolerite cutting the crinanite is sinuous, of variable thickness and splits and coalesces near the middle of the exposure to leave an “island” of crinanite. Studies have indicated that the analcite was derived from the alteration of nepheline. At the roadside opposite the northern end of the lay-by another 2 m thick quartz dolerite sill has 6 been intruded below the Dippen Sill. It displays very good chilled margins. A vein of basic glass can be seen at the southern end of the outcrop. 1700 Return to Hotel 1830 Dinner

OS Map (Not to scale) showing localities in the Levencorroch – Kildonan area

Dykes on the Foreshore near Kildonan

Friday 27th September 2019 0930 Check out from BW Kinloch Hotel, Blackwaterfoot 1000 Arrive Brodick Ferry Port 1105 Depart Brodick on Calmac Ferry 1200 Arrive Ardrossan Ferry Port Set off for Malvern (NB: Fastest route is firstly to go north towards Glasgow and join 1215 the M74) 19-2000 Arrive Malvern