Difference between revisions of "Craig Rossie - an excursion"

From Earthwise
Jump to navigation Jump to search
(No difference)

Revision as of 12:47, 29 May 2019

thumbnail
From: Browne, M.A.E. and Gillen, C. (editors) 2015. A geological excursion guide to the Stirling and Perth area. Edinburgh: Edinburgh Geological Society in association with NMS Enterprises Limited. Buy the book EGS.
Figure 14.1 Geological map of the area around Craig Rossie, showing localities for Excursion 14.

File:EGS_STIRL_PLA_14_01.jpg|thumbnail|Plate 14.1 Locality 14.1. Rhyodacite with brecciation and mineralisation, Pairney Quarry.]]

Plate 14.2 Locality 14.1. Rhyodacite with flow folds (centre) and green xenolith of rotted igneous rock, top left of notebook, Pairney Quarry.
Plate 14.3 Locality 14.3. Craig Rossie scarp and talus (scree).

Contents

Excursion 14 Craig Rossie

By Matt Armstrong and Mike Browne


Purpose: To examine a distinctive flow-banded rhyodacite lava in the Ochil Volcanic Formation (Arbuthnott–Garvock Group); to view the extensive landslips that have affected the eastern slopes of the hill.
Logistics: From Stirling, take the A9 to the western turn off to Auchterarder. In the village, where facilities are available, turn right at the east end along the B8062 Auchterarder–Dunning road, passing Pairney Farm [NN 977 131] and turning southwards about 200m farther east into the approach road to the large disused quarry south of Pairney. This excursion is suited to cars and small buses. Walking distance is around 10km on tracks and on grass and heather. Proper hill gear should be worn. A public footpath goes across the land belonging to Pairney Farm.
Maps OS 1:50,000 Sheet 58 Perth & Kinross; OS 1:25,000 Sheet 368 Crieff; BGS 1:50,000 Sheet 39E Alloa; locality map (Figure 14.1).

Craig Rossie is a prominent topographic feature on the northern edge of the Ochil Hills near Auchterarder. It is geologically notable on account of the distinctive flow-banded rhyodacite lava of Early Devonian age, which occupies its summit and north-western slopes. The locality is also of interest for the extensive landslip, which involves the rhyodacite on the eastern side of the hill. Craig Rossie is an SSSI and Geological Conservation Review (GCR) site (Stephenson et al., 1999), lying close to the boundary between the Ochil Volcanic Formation and the younger Scone Sandstone Formation, which occupies lower ground north of the hills. These rocks dip to the NW, towards the axis of the Strathmore Syncline. One of the youngest lavas in the Ochil sequence, this rhyodacite constitutes a lenticular mass, which dips below a trachyandesite lava on Thorny Hill, north of Pairney, the younger lava being interposed between the rhyodacite and the succeeding sandstone. The lavas of the Ochil Volcanic Formation comprise mainly basaltic andesites, with a lesser proportion of basalts, andesites and trachyandesites. There are also a small number of rhyodacites, of which the Craig Rossie lava is the most important, the best exposed and the most accessible. It typically has pale-grey feldspar phenocrysts (oligoclase) together with phenocrysts of biotite and quartz set in a fine-grained brown or pink matrix. Together with other felsic lavas in the northern Ochils, this unit differs greatly in appearance from the dominant basaltic andesites, which are darker in colour.

Locality 14.1 [NN 9770 1277] Pairney Quarry: rhyodacite

The quarry displays large faces in banded rhyodacite lava, which was quarried as a raw material in the manufacture of rock wool. It is currently being landfilled and has been used intermittently by the farmer for tipping. Also, by the nature of the rock, the main faces are unstable, and great care should be taken. The rock is locally brecciated, bleached and silicified (Plate 14.1). Veins of green malachite and xenoliths, 5–10cm across, of bright green, badly rotted porphyritic dioritic or gabbroic rock are found (Plate 14.2). The following description is taken from the GCR volume (Stephenson et al., 1999):

The Craig Rossie rhyodacite is brown, dull red or pink in colour. It contains phenocrysts, particularly of pale-coloured feldspar but also of quartz and biotite, in a fine-grained crystalline matrix. As far as is known, the rhyodacite is a single lava and no separate flow units have been recognised. Its most striking feature is the widespread occurrence of colour-contrasted flow banding due to subtle mineralogical differences. This flow-banding developed as the cooling magma passed through a viscous phase, developing folds just prior to solidification. The folds are usually open in form but locally become overfolded. Undeformed flow-banding is seldom parallel to the base of the flow. Other features noted include amygdales of calcite and red chalcedony near the supposed top of the rhyodacite and patches of fine-grained sedimentary rock, which have been recorded as infilling fissures or spaces between autobrecciated blocks near the base.

Locality 14.2 [NN 9755 1295] Pairney Burn

On returning to the quarry entrance descend westwards to the Pairney Burn and proceed upstream through the deep valley cut in the rhyodacite between Castle Craig to the east and Kay Craig to the west. Flow banding is well exposed in weathered exposures. In places on the east bank, close to the burn, flow lineation is visible on the planar flow surface.

Locality 14.3 [NN 9750 1265] Tributary burn.

Proceed upstream as far as the right-angled bend in the Pairney Burn south of Kay Craig. At this point a tributary gully, following a concealed NW-trending fault, descends from the SE. Amygdaloidal grey basaltic andesite lava, which underlies the rhyodacite of Castle Craig, is exposed on the NE side of the gully about half way up. The basaltic andesite, juxtaposed with rhyodacite thrown down on the SW side of the fault, contains patches of fine-grained sedimentary rock, a characteristic of Lower Devonian lavas of this composition. The sedimentary rock was formerly believed to represent the infillings of fissures in a flow breccia but more recent interpretations of such features suggest that they are peperitic textures resulting from the contact of magma with wet sediment. To the NW, the fault crosses the Pairney Burn, on a line extending west of the rhyodacite of Kay Craig. It again crosses the Pairney Burn downstream of Pairney, where it passes between the amygdaloidal upper part of the rhyodacite (not now exposed) and sandstones of the Scone Sandstone Formation (exposed near the railway bridge). There is a well-marked track at the head of the gully. To the left the track leads northwards back to the quarry through a glacial meltwater channel, which has been badly damaged by quarrying. In the opposite direction the track continues southwards along the east bank of the Pairney Burn.

There are two practicable routes to the top of Craig Rossie. The shorter and steeper diverges from the track a short distance south of the head of the gully, where a fence on the left of the track extends uphill in an ESE direction. This may be followed until it changes direction. Thereafter the route to the summit of Craig Rossie is south-eastwards above the line of crags on the SW side of the hill. The summit can be reached in about 40 minutes. There are few exposures on this route, but the views are extensive towards Ben Effrey, and to the active screes below the western and southern side of the summit of Craig Rossie (Plate 14.3). The second route continues along the track. Beyond a sharp bend in the course of the burn [NN 9758 1245], small exposures of rhyodacite on the uphill side of the track are not far above the unexposed base of this lava. The rock here is thrown down to the SW in relation to that on Craig Rossie by the NW-trending fault, which extends from the gully west of Castle Craig to pass east of an outlier of rhyodacite, also thrown down to the SW, which forms the summit of Ben Effrey. Opposite Upper Coul the outcrop of the base of the rhyodacite east of the Pairney Burn turns ESE to ascend the north bank of Green’s Burn [NN 9755 1205]. Here, underlying dark-grey amygdaloidal andesites are exposed on the south side, where the track crosses the burn.

Locality 14.4 [NN 9765 1160] Track-side

At a point on the track directly downhill from the southern end of the crags on Ben Effrey, there are exposures of a brecciated rock which contains a variety of inclusions, including fragments of pink felsic lava. This material is sporadically exposed as far as a gully that crosses the track at [NN 9785 1125]. Beyond this are exposures of grey porphyritic lava, succeeded to the south by further sporadic exposures of brecciated rock of silicic composition. A deeply rutted track, which forks left uphill before the Beldhill Burn is reached, may be followed to the top of Beld Hill [NN 9825 1080]. From here the summit of Ben Effrey, where there are the remains of a fort, lies about 500m along the ridge to the NE. If Ben Effrey is not visited, the route to Craig Rossie from Beld Hill is north-eastwards towards the western boundary of a forestry area. The forestry fence can be followed northwards along a broad ridge towards the summit of Craig Rossie.

Locality 14.5 [NN 9800 1150] Ben Effrey

On Ben Effrey the rhyodacite comprising the summit outlier is well exposed. South-west of the rhyodacite outcrop and a short way down the western slopes of the hill, there are exposures of a highly decomposed basalt dyke, which has been reduced to a brown sand in places, and areas of scree. The top of the hill is a fine viewpoint, the base of the rhyodacite ascending the SW face of Craig Rossie being especially prominent from here. There is also a good view towards the SW, where the transverse valley that carries the drainage of the valley of the Coul Burn into the Pairney Burn is conspicuous. From the summit of Ben Effrey the route to the forestry fence is first SE then eastwards, avoiding the valley of Green’s Burn.

Locality 14.6 [NN 9850 1212] Craig Rossie

There are rhyodacite crags both east and south of the summit of Craig Rossie, with extensive screes to the south. A grassy corridor descending between exposures south of the summit triangulation pillar marks the site of a NNW-trending fault, which throws down 10m to the east. From the lower ground south of the summit, it may be observed that the crags east of the fault descend to an appreciably lower level than do the rhyodacite exposures west of the fault.

Locality 14.7 [NN 9853 1207] East face of Craig Rossie: landslips

The east face of Craig Rossie, as seen from east of the summit, shows an upper line of rhyodacite crags, descending northwards and forming the edge of the unmoved mass of the hill (Plate 14.4). East of this line, a 400m-long slice of the lava has broken off and slid downhill to form a subparallel second rocky scarp at a lower level. The upper surface of the displaced mass is tilted backwards towards the hill, and joints in the rock, formerly vertical, now dip away from the hill, both effects being caused by rotation during movement. Rocky irregularities of the upper surface reflect differential movement of individual parts of the landslipped slice. To the north, other prominent rhyodacite masses have travelled farther downhill and they become more and more disorientated in this direction, resulting in a scene of chaotic disarray. Towards the bottom of the hill, near Tarnavie, the landslip terminates in completely broken material with large blocks of the lava carried forward on lobate projections, probably consisting in part of superficial deposits at the extreme limit of movement. There is no historical record of landslip activity, and it is probable that the principal movement was of Late Devensian age, following closely upon the final deglaciation of the area. The rock has broken away on planes, probably faults of north to NNW trend, and is likely to have involved the subjacent andesites, although none of this material has been detected in the landslip. The landslip lies within an enclosed, partly afforested, area. To return, follow the slopes beside the screes on the north side of Green’s Burn and back to the track.

Excursion 15 Perth

Mike Browne and Con Gillen

This excursion illustrates the Lower Devonian rocks of the Strathmore basin in the Perth area, which are volcanic rocks of the Ochil Volcanic Formation, overlain by sedimentary strata of the Scone Sandstone Formation. In the Stirling–Perth area, these rocks were folded during the mid-Devonian Acadian orogenic event to form part of the southern limb of the ENE-trending Strathmore Syncline and the northern limb of the Ochil–Sidlaw Anticline. Latest Carboniferous quartz-dolerite dykes intrude both of these formations. The mainly grey, fluviatile, channel sandstone bodies along with reddish-brown overbank or lacustrine silty mudstones are part of the sedimentary pile of the Strathmore basin. Bluck (1990) has expressed the view that this river system drained a mountainous area at some distance away, and since the continent–continent collision between Laurentia and


Purpose: To look at the Ochil Volcanic Formation (Arbuthnott– Garvock Group), including feldsparphyric basaltic andesite lavas, debris-flow conglomerates and interbedded fluvial and lacustrine strata; to examine the sedimentology of the overlying fluviatile Scone Sandstone Formation, from which the Stone of Scone was probably hewn; to view quartz-dolerite dykes.
Logistics: Access and parking for cars and small coaches is available near or at all localities, but some are not suited to larger coaches without much increased walking distances. Facilities are available in Perth at the South Inch. Health and Safety is a significant feature, in a working quarry and walking beside the River Tay. Access is freely available except to Friarton Quarry (Tarmac), where advance notice is required and the usual hard hat, etc. obligatory. If travelling from Stirling, follow the A9 into Perth via Friarton Bridge.
Maps OS 1:50,000 sheets 53 Blairgowrie and 58 Perth & Kinross; OS 1:25,000 Sheet 369 Perth & Kinross; BGS 1:50,000 Sheet 48W Perth; locality map (Figure 15.1).

This excursion illustrates the Lower Devonian rocks of the Strathmore basin in the Perth area, which are volcanic rocks of the Ochil Volcanic Formation, overlain by sedimentary strata of the Scone Sandstone Formation. In the Stirling–Perth area, these rocks were folded during the mid-Devonian Acadia orogenic event to form part of the southern limb of the ENE-trending Strathmore Syncline and the northern limb of the Ochil–Sidlaw Anticline. Latest Carboniferous quartz-dolerite dykes intrude both of these formations. The mainly grey, fluviatile, channel sandstone bodies along with reddish-brown overbank or lacustrine silty mudstones are part of the sedimentary pile of the Strathmore basin. Bluck (1990) has expressed the view that this river system drained a mountainous area at some distance away, and since the continent–continent collision between Laurentia and Baltica took place in Silurian times (the Scandian orogenic event), then it was possibly the Scandian mountains that provided the sediment for this river system.

Locality 15.1 [NO 1350 2334] Corsiehill Quarry: quartz-dolerite dyke, andesitic lava and horizontal slickensides

From the Friarton Bridge, leave the A90 at the north end to join the A85 Dundee Road into Perth. As the quarry is located on the northern side of Kinnoull Hill on Corsiehill Road, it is most easily accessed from the A85 by turning into Manse Road on the right, just before the left turn to the Queen’s Bridge. From Manse Road, a right turn leads to Corsiehill Road. There is ample parking in the old quarry and beside the road.

The quarry is excavated in an easterly trending generally medium-grained quartz-dolerite dyke of the Central Scotland Late Carboniferous Tholeiitic Dyke-swarm. It is intruded into feldspar-phyric andesitic lava flows of the Ochil Volcanic Formation. Most of the dyke has been worked out, leaving only patchy selvedges of fine-grained basalt dyke margin in contact with the andesitic lava on the north and south walls, but with its full width exposed in the west and east ends of the quarry. The quarry operated from before 1832 to after 1932 and is thought to have supplied roadstone aggregate. The youngest part of the workings was in the lava that is exposed in the embayments in the walls on the south side of the quarry. The lava at the entrance to the quarry looks slaggy and is vesicular; some of these cavities are filled with calcite, chlorite and quartz. The more-massive but jointed dolerite is best seen below the wooden steps at the west end of the quarry. The two margins of the dyke may be examined in the south wall beside the car park and in the north wall in the wooded area east of the car park. In both places subhorizontal polygonal joints are visible on the vertical faces, as is to be expected where hot magma is intruded into vertical cracks and chills in contact with cold country rocks. In this locality the lavas are about 410 million years old and the dyke 300 million years old. Note some spheroidal (onion skin) weathering of the quartz-dolerite in places. In the SE extension to the quarry, subhorizontal slickensides can be seen in the lava.

Locality 15.2 [NO 1366 2282] Kinnoull Hill: viewpoint geology, feldspar-phyric basaltic andesite flows

From the quarry, walk up Kinnoull Hill to the folly of Kinnoull Tower and the summit viewpoint. Follow the waymarked path to the west of the quarry uphill noting the andesitic lava knolls with large white feldspar phenocrysts (4mm) near the picnic tables at the start. From the top of the hill and the tower (Plate 15.1) there are excellent views south and east over the NE Fife Hills (Ochil Volcanic Formation), including Norman’s Law. The major break in slope on the north side of these hills marks the position of the large South Tay Fault that throws down to the north, with younger sedimentary rocks of the Upper Devonian and Lower Carboniferous under the low ground, mainly hidden by much younger Quaternary sediments. On the low ground, the River Tay is conspicuous and its confluence with the River Earn should be discernible. Also visible, except at or near high tide, are the modern intertidal deposits of the estuary. The terraces of the raised intertidal flats of the Holocene Carse Clay and the raised marine and beach deposits of Late Devensian age are part of this landscape tapestry.

The view east from the tower has featured in many Scottish calendars. The steep wooded cliffs of Kinnoull mark the position of a significant easterly trending fault, the Kinnoull Fault that throws down to the north. A similar fault forms the south side of Moncreiffe Hill. Both these faults connect to the North Tay Fault that throws down to the south. This fault, together with the South Tay Fault, form a small rift or graben on the crest of the Ochil–Sidlaw Anticline in which the younger rocks of the Upper Devonian and Lower Carboniferous are preserved. The view west from the tower is of the Ochil Hills, with Craig Rossie near Glen Eagles (Excursion 14) a distant feature. From the nearby summit viewpoint there is also a distant view of the Highlands and also, nearer, the ‘dry valley’ west of Perth of the Methven Gap, where about 14,500 years ago the retreat of glacier ice west to Crieff allowed the sea to form an embayment up the Earn valley to Crieff and east down this gap to Perth. On the return descent to the quarry, a good view is obtained of the Tay valley at Scone, with views to Dunkeld.

Locality 15.3 [NO 1200 2520] Quarrymill: Scone Sandstone Formation

Quarrymill Woodland Park lies on the A93 (Perth to Blairgowrie Road), just south of Scone Palace on the east side of the River Tay opposite Perth (conveniently reached from Corsiehill Quarry). It has three waymarked walks and wheelchair accessible facilities. All start from the car park. Both the Millstone and Mill Pond routes are suitable for wheelchair users and have viewing platforms and picnic areas. The voluntarily staffed coffee shop is currently open Mon–Sat: 10am–4.30pm from the end of April to the end of September. Along the path at [NO 1232 2532] is a 45m-long cliff, showing pale-red micaceous sandstone with cross-bedding. The colour of the sandstone is much paler at [NO 1226 2528]. Historic records call the quarries at this site ‘Balcormac’ and possibly also ‘Kincarrathie’, as no rock is known to crop out at or near the house of that name.

The best of the rather limited geology is to be seen from the path in small cliffs beside the Annaty Burn and in the Annaty waterfall. On the west side of the wood are overgrown and landscaped quarries from which stone was thought to have been worked for Scone Abbey and Palace, the old Perth bridges and very likely the Stone of Scone (Stone of Destiny) now housed in the Regalia Room in Edinburgh Castle. The Stone appears to be made of sandstone local to Scone. A smaller scale replica of is located on Boot Hill in front of Scone Palace. Evidence provided by Fortey et al. (1998) about the Stone includes petrological descriptions of sandstone from Quarrymill, Lethendy, Huntingtower, Letham House, Crossgates and Kingoodie (Invergowrie), and is consistent with the suggestion that it came from Quarrymill.

Locality 15.4 [NO 1141 2580] River Tay at Scone Palace

From Quarrymill, turn right out of the car park and travel north, passing the main entrance to Scone Palace, then turn left on to the Stormontfield Road at Old Scone. About 400m on, turn left [NO 1136 2734] on the track down to the active Salmon Bothy [NO 1056 2656] beside the River Tay and seek permission to park. Note that access by car will be almost impossible during public events, when vehicles will be parked on the riverbank, almost to the exposure. The locality is a 1.3km walk SE of here, beside the river.

Most of this exposure is as rock reefs in the river bed. It is neither visible nor accessible when the river is in flood or even just bank full. Care needs exercising so close to this major river. This locality provides the opportunity to compare these old river deposits with the modern ones of the Tay. In this reach of the river, there is an island with one channel usually almost dry. Here the gravel bed of the river is well seen with gravel bar features in the dry channel and imbrication of the gravel is seen after floods.

The exposures, which start at [NO 1141 2580] and end at [NO 1154 2554], are well worth visiting unless a lot of slime covers the rocks from agricultural pollution by farm fertilisers. The Scone Sandstone Formation here consists of reddish purple sandstone and some conglomeratic beds of fluvial origin. The clasts, up to cobble and boulder size, consist of concretionary limestone (‘cornstone’) known as calcrete [NO 1147 2564]. Such deposits form as part of a soil profile in a semi-arid climate with wet and dry seasons. As the groundwater table rises and falls, the salts in the sediments are leached downwards to form nodules that may coalesce to form rubbly beds of calcrete. In subsequent times of severe flood, the calcrete is eroded and transported as gravel. At this locality, confusingly, some calcrete nodules also occur in situ in the sandstones. Rare clasts of lava and quartz and more commonly of red and green mudstone may also be seen. Trough cross-bedding is present in the sandstones (Plate 15.2), well seen at [NO 1143 2574], near a fisherman’s hut. Whereas most of the sandstones were laid down in sand bars in a braided river, the clay clasts are the remnants of overbank floodplain deposits destroyed in flood events.

Locality 15.5 [NO 1160 2134] Friarton Quarry: Ochil Volcanic Formation, autobreccia, interbedded sedimentary rocks, quartz-dolerite dykes

From Scone Palace, return to Perth and cross the Tay to the west bank at the Victoria Bridge. Turn left (south) and then right at the Fergusson Gallery and follow the A912 from the traffic lights at the north end of the South Inch, passing Perth Prison. Turn right uphill at the end of the housing on the western side of the road in south Perth [NO 1160 2150]. This road leads shortly on the left to the entrance to the quarry [NO 1136 2150]. This quarry is still working (Tarmac) after more than 70 years but perhaps of limited future. How the faces will remain should the quarry close is not known, but they may provide an opportunity for provision of conservation sections. Strict health and safety controls apply to visitors, who are not allowed within set distances of the base of faces and from their top edges, the latter normally guarded by high artificial ridges. Full personal protective clothing is essential (including hard hat, long sleeved yellow jacket, eye protection, and footwear with hard toe-caps and ankle protection).

From near the site office there is a good view of the Tay valley and the wooded scarp formed by the Ochil Volcanic Formation at Kinnoull Hill. The face of the hill is the position of a major fault that throws down to the north. There are excellent views south and east over the NE Fife Hills (also Ochil Volcanic Formation), including Norman’s Law. Also well seen is the low ground beside the River Tay, with the terraces of the Holocene Carse Clay and the raised marine and beach deposits of late-Devensian age. The view west is of the Ochil Hills.

The quarry exposes andesitic lava flows, up to 15–20m thick, and interbedded sedimentary rocks consisting of siltstones, mudstones and sandstones in which lava grains are a significant component, all belonging to the Ochil Volcanic Formation (Plate 15.3). Baked mudstone can be seen immediately beneath the lava at [NO 1145 2105]. The lava at this point is heavily veined with bright green malachite. Two or three easterly trending late-Carboniferous quartz-dolerite dykes cross-cut these rocks. The best-exposed dyke is about 35m wide and is easily traceable in the quarry floor and east wall. On the west side, the dyke is finer grained, veined and shows green-coloured hydrothermal effects [NO 1136 2112]. It is generally medium grained but is fine grained (i.e. basalt) at the contacts with the country rock. Feldspar and pyroxene grains are identifiable as the main mineral component. Subhorizontal cooling joints (as at Locality 15.1, Corsiehill) are visible in the sections.

Brecciated andesitic rock is well exposed in the NE part of the site, just above the contact with sedimentary rock [NO 1168 2115]. A fertile discussion on the origin of the coarse breccia would consider possible origins but noting that mineralisation of the voids is also seen (calcite and baryte). The rock may be autobrecciated lava with the cavities infilled by sedimentary rock; the waterlain deposit laid down by percolating flow of groundwater.

Two further interpretations require that the wet sediment is laid down first and then either hot magma flows over the deposit as lava or is intruded into it as a sill. In both cases there is a violent interaction between the magma and the wet sediment producing the breccia and disrupting the bedding of the sediments by fluidisation; such breccia is known as peperite (Plate 15.4).

In the southern part of the quarry, several (up to 10?)m of well-bedded, purplish and greenish grey siltstones, mudstones and sandstones may be inspected. They show flat bedding and ripple cross-bedding. Rip-up clasts are present in the coarser beds and locally small granule (grit sized) lava fragments form fine conglomerates. The bedding is inclined at about 16° to the NW, reflecting the position of the quarry, which is located on the NW limb of the Sidlaw–Ochil Anticline, a major Mid-Devonian (Acadian Orogenic event) fold structure. Careful search of the finest rocks may produce examples of trace fossils in the form of trackways of unknown arthropod animals. Red hematite-stained plant remains are present in the greenish grey siltstones. Other sedimentary features include small sand dykes, desiccation cracks and load casts. The commonly seen small faults have associated hematitic staining, e.g. in the SW corner at [NO 1139 2095].

Excursion 16 Perth: building stones

Donald MacIntyre, Rhoda Fothergill, Mike Browne and Con Gillen


Purpose: To examine some of the most-important historical buildings and most-interesting examples of the uses of building stones in the historic centre of Perth.
Logistics: This half-day walking excursion starts at St John's Kirk and finishes in West Mill Street. Toilets are available in South Street near the start of the excursion and the west end of Mill Street near the end.

As this excursion is in a busy city centre, care must be taken when walking and looking at buildings. Saturdays in particular can be very congested, with only parts of the route pedestrianised. Note that façades may be altered, and also there are changes of use of buildings that can affect the visible geological features.

Mapslocality map (Figure 16.1).

Traditional Perth building materials were derived from local andesite and basalt lavas of the Ochil Volcanic Formation and sandstones of the Scone Sandstone Formation. Other sources used included quartz-dolerite dykes that intrude these rocks, as at Corsiehill Quarry (Excursion 15). Other materials include red sandstones of the Glenvale Sandstone Formation around Bridge of Earn and in the Carse of Gowrie. Late-glacial marine clays (14,500 years old) were used for brick making at Errol until recently. Metamorphic rocks from the Dalradian north of the Highland Boundary Fault include roofing slates from Dunkeld and Logiealmond.

Until the arrival of the railways in 1848, Perth was largely confined to the low ground west of the Tay. Without crossing to the east bank for Quarrymill, the nearest source of building stone was on the higher ground of the Burgh Muir, where sandstone was quarried until the twentieth century at the now infilled Burghmuir and Newhouse quarries. Because transportation was downhill and did not involve crossing the river, the Burghmuir Quarry [NO 0830 2385] was a possible source when stone was first used for Perth buildings in medieval times. The earliest record of stone being brought in is 1379, when Robert II arranged for stone for his monument to be taken from Leith by sea. As the Tay was navigable as far as the High Street, it would have been easy to bring stone from Kingoodie, near Dundee, or from farther afield. In 1651, Oliver Cromwell built one of his five great Scottish fortresses in Perth, in the process demolishing older buildings that could provide stone for his citadel on the South Inch.

Locality 16.1 [NO 1195 2355] St John’s Kirk

This is the oldest building in Perth (Plate 16.1); it is sometimes open to visitors and guided tours may take place. It was granted to Dunfermline Abbey in 1126, but nothing of the earlier building remains above ground. If the three consecration crosses in the choir are correctly identified, that part of the kirk had been built before 1242. The stones in the choir are smaller, less regular in shape, and less well finished than those in the nave. All appear, however, to be of local Scone Sandstone Formation, from the supposed quarries at Kinharrachie (Kincarrathie) and Balcormac. This may have been at the request of Robert the Bruce in 1328. The rather massive sandstones in the kirk were from Quarrymill. The pillars in the nave are noticeably simpler than those in the choir. About 1400 the Chapel of St James, on the south side of the kirk, was repaired, and in 1440 funds were assigned for building the choir and porch of the church. About the same time the names of Bailie John Fuller and his wife, no doubt donors, were commemorated on the pillar towards the SE end of the choir, and a reference in 1448 to the new choir of the parish church shows that this part of the kirk was completed by about 1450. The nave was completed by 1500 and the central tower before 1511. The vaulting in the porch of the Halkerston Tower is fifteenth century. A programme of repairs to the nave began in 1598, and the north transept was shortened in 1823, to widen St John’s Place. Sir Robert Lorimer was responsible for a major restoration of the kirk in 1923–26.

There are many examples of pebbles in the exterior walls of the kirk, and there are some in the interior walls, e.g. to the left of the door leading from the nave to the Halkerston Tower. Clay pellets or rip-up clasts are common in Perth’s older buildings: good examples are visible on the second buttress from the east end of the exterior north wall of the kirk, and the SE corner of the base of the great pillar at the NW corner of the crossing. Some of the setts in the streets beside St John’s Kirk and the City Hall are fine-grained igneous rock. A few other setts, such as some of those in Flesher’s Vennel and its extension into South St John’s Place, are blocks of imported granite. Those now on the west pavement of Tay Street came from China.

Locality 16.2 [NO 1185 2355] The City Hall

Just west of St John’s Kirk is the disused baroque-style City Hall with ionic pillars (Locality 16.2a) (Plate S.13). It was completed in 1914 and is made of a uniform, rather fine-grained greyish sandstone with numerous examples of truncated cross-bedding and one or two examples of contorted beds (soft-sediment deformation) resulting from the escape of water during the compaction of what were once loose sand layers at the bottom of a river. The best place to look for these is near the SE corner of the building. The texture and colour of this rock differ from that of the Sheriff Court, or indeed of other buildings on Tay Street. According to The Perthshire Advertiser, 1911, the City Hall is ‘built of bluish grey stone from Leoch Quarries, Forfarshire’. The Leoch Quarry [NO 359 361] near Dundee was still being worked in 1952 (Armstrong et al., 1985) and is in the Dundee Flagstone Formation. Across the road, at the west end of the City Hall, is the King Edward VII Memorial, a model based on Edinburgh’s Mercat Cross, and also the well-sculptured and hybrid-styled Salvation Army building (1904) on South Street, built in Permian red sandstone. Locality 16.2b [NO 1197 2360], Clydesdale Bank nos 3–5 (1845?), is a modest building with ionic pillars and Locality 16.2c [NO 1200 2350] Bank of Scotland nos 48– 50 (1847) in John Street (Plate 16.2) is in grand Italianate renaissance style; both are of Carboniferous sandstone.

Locality 16.3 [NO 1194 2372] Old City Wall

From here walk north to High Street, cross and find the narrow entrance of Albert Close/Skinnergate on the left. A ‘primitive’ wall forms the north side of Albert Close, between George Street and the north end of Skinnergate. It is on the line of the original defensive wall, which used the city lade as a moat, but lacks the strength required for defence. A conspicuous feature of the wall is the variety of rock types used. Different sizes and shapes of sandstone are common, mainly small slabs split along prominent bedding planes and a few rounded boulders of massive sandstone. Of particular interest are clusters of water-rounded quartzite, ‘greenschist’ and garnet schist, probably from the beach at the north end of Friarton (Moncreiffe) island. This is the only known Perth wall that incorporates Highland rocks.

Locality 16.4 [NO 1203 2357] The Watergate

Return to the High Street and turn left, cross and walk east to the Watergate and turn right (south). No. 27 in the Watergate bears the date 1725, and although commemoration stones of this kind can be re-used at later dates, there is no reason to doubt this is the date of construction. Unfortunately, here and in a number of other buildings, the walls have been plastered and painted so that the stone work is concealed. The date 1780 is found high on the gable of the first building on the west side of George Street at its junction with the High Street. Here also the stonework is concealed. Uncoursed walls made of random rubble (rough and ready local sandstone) can be seen in the backs of some buildings in the city centre: for example, some with frontages on George Street, St John’s Street, and St John’s Place. Return to the High Street, turn right and then left (northwards) at the riverside to Perth (Smeaton) Bridge.

Locality 16.5 [NO 1202 2385] Smeaton Bridge

Stone from Quarrymill was shipped downstream to build Smeaton Bridge (Locality 16.5a). Work began in 1766 and was completed in 1771. The bridge, to which there is easy access at the west abutment, displays good examples of purplish red stone from the Scone Sandstone Formation (Plate 16.3). Many water-rounded pebbles of older rocks, including local Devonian lava and quartzite and vein quartz from the Highlands, are scattered through the red sandstone matrix. These sandstones are typical fluviatile deposits, that is, sandbars in braided rivers. The original sediments may have been flash-flood deposits; they are cross-bedded and poorly sorted. The circular features (spandrels, between the arches) are black basalt. Note the marks recording levels of the larger floods that have inundated Perth over the centuries; the last two in 1990 and 1993 resulted in the completed major flood prevention scheme. The pillars of the new flood gates (Locality 16.5) on the North Inch adjacent to the Smeaton Bridge consist of pale-red Dumfries Permian sandstone (presumably Locharbriggs Quarry), displaying the fine layering and uniform constitution found in a sand dune. The statue of Prince Albert (Locality 16.5c) [NO 1190 2390] nearby on the North Inch (1864) is of cross-bedded Carboniferous sand-stone from Redhall Quarry, Edinburgh (Gullane Formation). The statue rests on local sandstone that displays cross-bedding, with blocks both right and wrong way up.

Locality 16.6 [NO 1230 2354] Kinnoull Parish Church

Return to Smeaton Bridge, cross to the east side of the river and turn right (south) along Gowrie Street for about 400m to the next localities. The church, on the west side of Gowrie Street, was built in 1826 in Gothic style with quality ashlar stonework. The stone is cross-bedded Scone Sandstone containing pebbles of lava and limestone, as well as clay clasts, and shows decorative chisel marks. The east-facing buttress of the north doorway shows two sets of cross-beds indicating currents coming from the left. They are right way up, and between them is a layer containing red mud flakes.

Locality 16.7 [NO 1235 2350] Kinnoull Primary School

Almost opposite the church stands Kinnoull Primary School, built in 1876 in plain Greek style. The building is in a reddish sandstone, with buff-coloured sandstone at the corners and around the doors and windows. The red stone has been decorated by chiselling that makes it difficult to see the internal structure of the rock, but several blocks contain flakes of reddish clay fragments up to 10cm long. Some of the buff-coloured sandstone blocks are cross-bedded. The school occupies the site of the former Witch Quarry, a local source of basalt. This volcanic rock, with angular joints and gas cavities (vesicles) is well exposed at and near the north end of the site. Beside the pavement, the rock has been cemented over to prevent rockfall onto the road. The basalt was used extensively in walls along the Dundee Road between the Smeaton Bridge and Branklyn Garden. In places, dressed rectangular blocks are incorporated in the walls, but lava has rarely been used for building in Perth.

Locality 16.8 [NO 1226 2342] Queen’s Bridge

Continue southwards along Gowrie Road and turn right (west) onto Queen’s Bridge. The old bridge (Victoria Bridge) was jacked up by 2m during the construction of the replacement concrete bridge. In the northern approach, walls at the east end are grey Carboniferous sandstone blocks showing cross-bedding, soft-sediment deformation and fine conglomerate beds (grit). Quartz clasts up to 1cm are present; this stone is not local and may have come from the Glasgow or Denny area.

Locality 16.9 [NO 1231 2332] Kinnoull Aisle

From the south side of the bridge enter the riverside gardens and head south to the walled enclosure of the graveyard. The only remains of old Kinnoull Church are in the small, almost square aisle (sometimes open during the summer), now a vault with a modern steep, gable-ended roof. In the east wall is a doorway with an armorial panel over it. The Kinnoull family keep the building in good repair. Their burial vault is beneath the floor and the monument to the First Earl of Kinnoull, Lord Chancellor Hay is within. The stone in the building is of local red-brown Scone Sandstone and thin blocks of Ochil Volcanic Formation volcaniclastic sandstone and siltstone that spall badly. The church was built before 1361, when it was granted to Cambuskenneth Abbey, then rebuilt in 1779 and demolished in 1826.

Locality 16.10 [NO 1210 2357] St Matthew’s Church

Return to the Queen’s Bridge and turn left to go back to the west bank of the river. Turn right into Tay Street. Most of the stone for the Gothic St Matthew’s Church, built in 1871, came from Huntingtower Quarry. This quarry was excavated in Scone Sandstone Formation, like Quarrymill, Burghmuir and Newhouse. The yellowish sandstone around the door may be of Carboniferous age.

Locality 16.11 [NO 1207 2340] Sheriff Court

Remaining on the west side of Tay Street, walk south to the Sheriff Court, built in 1822 in the Greek style, using columns originally intended for Broomhall, Charlestown, Fife. The stone may have come from Carboniferous rocks in Fife or the Lothians. While many of Perth’s grey sandstones show cross-bedding, it is particularly obvious on this building. The parking area behind the court was formerly the County Prison. It was built with quartz-dolerite from Lamberkine Quarry (1km west of bypass). Records show that this rock (a dyke) was once an important source of building stone. The quartz-dolerite, seen in the walls of the former prison around the parking area, is black when fresh and weathers to a rusty surface (Plate 16.4).

Locality 16.12 [NO 1204 2311] J. D. Fergusson Gallery (old water cistern)

This building on Tay Street, at the junction with Marshall Place, was formerly the local water works. Filtered clean water was pumped from Moncreiffe Island to its cast-iron cistern. Adam Anderson’s Roman Doric design (1802) was converted to an art gallery in 1992. It is mainly in blonde Carboniferous sandstone with cross-bedding and soft-sediment deformation; the rear is partly in local reddish brown Scone Sandstone with large red-brown mudstone rip-up clasts.

Locality 16.13 [NO 1165 2370] and [NO 1170 2372] Sandeman Building and Gloag Building

From here, head west along Marshall Place, noting terraced properties showing subsidence damage. At the junction with Scott Street, turn right (north) and walk for about 500m to the Sandeman Building (former public library, Plate 16.5) and the former Gloag Building on Kinnoull Street. Both are in red cross-bedded sandstone. The opening of the railway in 1848 made possible the transportation of this superior Permian rock from Locharbriggs (Dumfries) to Perth. This sandstone, much of it deposited in desert dunes, has individual grains that are more rounded than those from a water-lain variety, and have a frosted surface appearance. The grains are coated with iron oxide (hematite), which accounts for the red colour. The former St Paul’s Church (1807) on Old High Street and South Methven Street, with its octagonal design, is however of pebbly sandstone (Scone Sandstone).

Locality 16.14 [NO 1145 2373] Perth City Mills

From here turn left (west) into Mill Street. The mills, on West Mill Street, are built of Scone Sandstone, showing typical features such as cross-bedding, clay clasts, and pebbles of quartz, lava and limestone. Presumably the Burghmuir/Newhouse quarries supplied this stone. These buildings have been restored in the last 40 years, including as a hotel, formerly the Upper City Mills and granary (1792) and tourist information centre in the Lower City Mills (completed 1805). The old city lade is visible here, formerly powering the working external undershot water wheel in the Lower Mills. Two undershot wheels are visible under the foyer of the hotel.

At all times follow: The Scottish Access Codeand Code of conduct for geological field work