Thornhill – an excursion - Revision history

Scotfot at 19:44, 6 November 2015

2015-11-06T19:44:10Z

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	By A A McMillan. Excursion 2. From: Stone, P (editor). 1996. Geology in south-west Scotland: an excursion guide. Keyworth, Nottingham: British Geological Survey		By A A McMillan. Excursion 2. From: Stone, P (editor). 1996. [[Geology in south-west Scotland: an excursion guide\|Geology in south-west Scotland: an excursion guide.]] Keyworth, Nottingham: British Geological Survey

	== Thornhill: a small Permo-Carboniferous basin ==		== Thornhill: a small Permo-Carboniferous basin ==

Scotfot: /* 4 Enterkin Burn: early Namurian marine mudstone */

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4 Enterkin Burn: early Namurian marine mudstone

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	Aspects of the fauna are common to the north margin of the Thornhill Basin and the Sanquhar Basin to the north (Davies, 1970), suggesting that in the late Carboniferous the marine influence of the Midland Valley was being felt as far south as Thornhill.		Aspects of the fauna are common to the north margin of the Thornhill Basin and the Sanquhar Basin to the north (Davies, 1970), suggesting that in the late Carboniferous the marine influence of the Midland Valley was being felt as far south as Thornhill.

			===References===

			<References/>
	{{EGwalks}}		{{EGwalks}}
			[[Category:6. The South of Scotland]]

	[[~~category~~:6. The South of Scotland]]

Scotfot: /* 4 Enterkin Burn: early Namurian marine mudstone */

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4 Enterkin Burn: early Namurian marine mudstone

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	==== 4 Enterkin Burn: early Namurian marine mudstone ====		==== 4 Enterkin Burn: early Namurian marine mudstone ====
			[[File:ThornhillEnterkinBurnExcursionMap.jpg\|thumbnail\|Enterkin Burn (Locality 4: Enterkin Mudstone Formation) .]]
	Enterkin Burn, about 3 km NNW of Jenny Hair's Bridge, exposes fossiliferous Carboniferous strata resting unconformably on Ordovician turbidites at the northern extremity of the Thornhill Basin. Limited car parking is available at the junction (NS 874 046) between the farm track to Inglestone and the footpath to Wanlockhead (Figure 17). From here visitors should proceed north on the Wanlockhead track for about 0.5 km before descending westwards down the steep valley side of the Enterkin Burn.		Enterkin Burn, about 3 km NNW of Jenny Hair's Bridge, exposes fossiliferous Carboniferous strata resting unconformably on Ordovician turbidites at the northern extremity of the Thornhill Basin. Limited car parking is available at the junction (NS 874 046) between the farm track to Inglestone and the footpath to Wanlockhead (Figure 17). From here visitors should proceed north on the Wanlockhead track for about 0.5 km before descending westwards down the steep valley side of the Enterkin Burn.

Scotfot: /* 3 Jenny Hair's Bridge, Durisdeer: Permian lavas, breccias and sandstones */

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3 Jenny Hair's Bridge, Durisdeer: Permian lavas, breccias and sandstones

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	==== 3 Jenny Hair's Bridge, Durisdeer: Permian lavas, breccias and sandstones ====		==== 3 Jenny Hair's Bridge, Durisdeer: Permian lavas, breccias and sandstones ====
			[[File:ThornhillJennyHairsBridgeExcursionMap.jpg\|thumbnail\|Jenny Hair's Bridge (Locality 3: Permian sandstone, breccia and basalt).]]
	Some 7 km north of Thornhill near the north margin of the Thornhill Basin, sections at Jenny Hair's Bridge provide a good opportunity to see some of the basal Permian sedimentary rocks and lavas. Limited car parking is possible at Jenny Hair's Bridge (NS 886 024) on the road leading from the A702 to Durisdeer (Figure 16). From the bridge a short round trip of 0.5 km downstream along the Carron Water enables the principal lithologies to be examined. This and several other localities are described in a field guide by Brookfield (1981). In this northern part of the basin and in the small outlier of Locherben to the east (Figure 13) the basal Permian strata comprise stream-flood breccias interbedded with thin olivine-basalt lava flows of the Carron Basalt Formation. The overlying breccias, fluviatile sandstones and siltstones of the Durisdeer and Locherben Breccia formations (Brookfield, 1978, pp.132-134; 1980, p.191, figs. 5 and 7) are interpreted as sheetflood desert floor deposits. These pass up into aeolian dune sandstones, the Thornhill Sandstone Formation, as seen previously at Locality 2.		Some 7 km north of Thornhill near the north margin of the Thornhill Basin, sections at Jenny Hair's Bridge provide a good opportunity to see some of the basal Permian sedimentary rocks and lavas. Limited car parking is possible at Jenny Hair's Bridge (NS 886 024) on the road leading from the A702 to Durisdeer (Figure 16). From the bridge a short round trip of 0.5 km downstream along the Carron Water enables the principal lithologies to be examined. This and several other localities are described in a field guide by Brookfield (1981). In this northern part of the basin and in the small outlier of Locherben to the east (Figure 13) the basal Permian strata comprise stream-flood breccias interbedded with thin olivine-basalt lava flows of the Carron Basalt Formation. The overlying breccias, fluviatile sandstones and siltstones of the Durisdeer and Locherben Breccia formations (Brookfield, 1978, pp.132-134; 1980, p.191, figs. 5 and 7) are interpreted as sheetflood desert floor deposits. These pass up into aeolian dune sandstones, the Thornhill Sandstone Formation, as seen previously at Locality 2.

Scotfot: /* 2 Crichope Linn: Coal Measures and Permian strata */

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2 Crichope Linn: Coal Measures and Permian strata

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	==== 2 Crichope Linn: Coal Measures and Permian strata ====		==== 2 Crichope Linn: Coal Measures and Permian strata ====
			[[File:ThornhillCrichopeLinnExcursionMap.jpg\|thumbnail\|Crichope Linn (Locality 2: Coal Measures and Thornhill Sandstone Formation).]]
	Crichope Linn lies 3 km east of Thornhill and about 4 km north of Croalchapel. 'Me Linn is approached by a well-marked path from the narrow road linking Gatelawbridge with Closeburnmill. An area nearby at the back of Newton Quarry (NX 907 955) (Figure 15), one of several old sandstone quarries at Gatelawbridge, serves as a parking place for several cars. It is also possible to take a coach to this locality but note that the roads are narrow and single tracked.		Crichope Linn lies 3 km east of Thornhill and about 4 km north of Croalchapel. 'Me Linn is approached by a well-marked path from the narrow road linking Gatelawbridge with Closeburnmill. An area nearby at the back of Newton Quarry (NX 907 955) (Figure 15), one of several old sandstone quarries at Gatelawbridge, serves as a parking place for several cars. It is also possible to take a coach to this locality but note that the roads are narrow and single tracked.

Scotfot: /* 1 Park Quarry, Croalchapel: Closeburn Limestone Formation */

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1 Park Quarry, Croalchapel: Closeburn Limestone Formation

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	`... so general was the opinion of the injurious consequences of lime laid on the ground for agricultural purposes, that the proprietor, in order to introduce its use, obliged his tenants in their leases, to lime a certain quantity of land yearly, he furnishing the lime, and even paying for the carriage; and the tenants for their parts, were bound to pay 5s. additional rent for every 80 measures of lime, the quantity considered sufficient for an acre.'		`... so general was the opinion of the injurious consequences of lime laid on the ground for agricultural purposes, that the proprietor, in order to introduce its use, obliged his tenants in their leases, to lime a certain quantity of land yearly, he furnishing the lime, and even paying for the carriage; and the tenants for their parts, were bound to pay 5s. additional rent for every 80 measures of lime, the quantity considered sufficient for an acre.'
			[[File:ThornhillParkQuarryExcursionmap.jpg\|thumbnail\|Park Quarry (Locality 1: Closeburn Limesrone Formation).]]
	Unfortunately the limestones are no longer visible but the upper part of the Closeburn Limestone Formation, of Lower Carboniferous (Brigantian) age, can be examined in Park Quarry. On accessing the quarry, '''proceed carefully '''to the degraded quarry faces near the remains of the old water wheel. Note also that the deep, '''steep-sided quarry hole is water-filled so '''stay well clear. The exposed strata comprise thinly bedded micaceous sandstone and siltstone overlying red and fossiliferous, micaceous silty mudstone. The strata dip gently east into the quarry face.		Unfortunately the limestones are no longer visible but the upper part of the Closeburn Limestone Formation, of Lower Carboniferous (Brigantian) age, can be examined in Park Quarry. On accessing the quarry, '''proceed carefully '''to the degraded quarry faces near the remains of the old water wheel. Note also that the deep, '''steep-sided quarry hole is water-filled so '''stay well clear. The exposed strata comprise thinly bedded micaceous sandstone and siltstone overlying red and fossiliferous, micaceous silty mudstone. The strata dip gently east into the quarry face.

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	Coal had to be brought for the kilns from Sanquhar or further afield for, although the Thornhill Basin contains Coal Measures, no coal is present.		Coal had to be brought for the kilns from Sanquhar or further afield for, although the Thornhill Basin contains Coal Measures, no coal is present.
	=		=

	==== 2 Crichope Linn: Coal Measures and Permian strata ====		==== 2 Crichope Linn: Coal Measures and Permian strata ====
	Crichope Linn lies 3 km east of Thornhill and about 4 km north of Croalchapel. 'Me Linn is approached by a well-marked path from the narrow road linking Gatelawbridge with Closeburnmill. An area nearby at the back of Newton Quarry (NX 907 955) (Figure 15), one of several old sandstone quarries at Gatelawbridge, serves as a parking place for several cars. It is also possible to take a coach to this locality but note that the roads are narrow and single tracked.		Crichope Linn lies 3 km east of Thornhill and about 4 km north of Croalchapel. 'Me Linn is approached by a well-marked path from the narrow road linking Gatelawbridge with Closeburnmill. An area nearby at the back of Newton Quarry (NX 907 955) (Figure 15), one of several old sandstone quarries at Gatelawbridge, serves as a parking place for several cars. It is also possible to take a coach to this locality but note that the roads are narrow and single tracked.

Scotfot: /* Introduction */

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Introduction

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	=== Introduction ===		=== Introduction ===
			[[File:ThornhillExcursionMap.jpg\|thumbnail\|Upper Palaeozoic strata of the Thornhill Basin and outliers - excursion map.]]
	At Thornhill (Figure 13) rocks of Permian and Carboniferous age occupy a fault-bounded basin orientated north–south and 18 km long (Pringle and Richey, 1931). Smaller outliers, which once formed part of a larger basin, are present to the east. The highest of these (presumed to be Coal Measures) lies some 350 m above sea level. The basin forms an important link between the Solway and Midland Valley basins (Figure 8). A particularly interesting transition is seen within the Lower Carboniferous sequence, where lithological variation at the northern and southern margins of the Thornhill basin may indicate differences in sedimentation imposed by local barriers to marine transgression. Other interesting features include a recognizable Coal Measures sequence, comparable with that in the adjacent Sanquhar Basin to the north, but thinner and without the coals. Excellent examples of Permian desert dune sandstones, basalt lavas and alluvial channel deposits can also be seen.		At Thornhill (Figure 13) rocks of Permian and Carboniferous age occupy a fault-bounded basin orientated north–south and 18 km long (Pringle and Richey, 1931). Smaller outliers, which once formed part of a larger basin, are present to the east. The highest of these (presumed to be Coal Measures) lies some 350 m above sea level. The basin forms an important link between the Solway and Midland Valley basins (Figure 8). A particularly interesting transition is seen within the Lower Carboniferous sequence, where lithological variation at the northern and southern margins of the Thornhill basin may indicate differences in sedimentation imposed by local barriers to marine transgression. Other interesting features include a recognizable Coal Measures sequence, comparable with that in the adjacent Sanquhar Basin to the north, but thinner and without the coals. Excellent examples of Permian desert dune sandstones, basalt lavas and alluvial channel deposits can also be seen.

Scotfot at 15:48, 29 March 2015

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← Older revision		Revision as of 16:48, 29 March 2015
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	By A A McMillan. From: Stone, P (editor). 1996. Geology in south-west Scotland: an excursion guide. Keyworth, Nottingham: British Geological Survey		By A A McMillan. Excursion 2. From: Stone, P (editor). 1996. Geology in south-west Scotland: an excursion guide. Keyworth, Nottingham: British Geological Survey

	== Thornhill: a small Permo-Carboniferous basin ==		== Thornhill: a small Permo-Carboniferous basin ==

Scotfot: /* = 2 Crichope Linn: Coal Measures and Permian strata */

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= 2 Crichope Linn: Coal Measures and Permian strata

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	Coal had to be brought for the kilns from Sanquhar or further afield for, although the Thornhill Basin contains Coal Measures, no coal is present.		Coal had to be brought for the kilns from Sanquhar or further afield for, although the Thornhill Basin contains Coal Measures, no coal is present.
	=		=
	==== 2 Crichope Linn: Coal Measures and Permian strata ===		==== 2 Crichope Linn: Coal Measures and Permian strata ====
	Crichope Linn lies 3 km east of Thornhill and about 4 km north of Croalchapel. 'Me Linn is approached by a well-marked path from the narrow road linking Gatelawbridge with Closeburnmill. An area nearby at the back of Newton Quarry (NX 907 955) (Figure 15), one of several old sandstone quarries at Gatelawbridge, serves as a parking place for several cars. It is also possible to take a coach to this locality but note that the roads are narrow and single tracked.		Crichope Linn lies 3 km east of Thornhill and about 4 km north of Croalchapel. 'Me Linn is approached by a well-marked path from the narrow road linking Gatelawbridge with Closeburnmill. An area nearby at the back of Newton Quarry (NX 907 955) (Figure 15), one of several old sandstone quarries at Gatelawbridge, serves as a parking place for several cars. It is also possible to take a coach to this locality but note that the roads are narrow and single tracked.

Scotfot: /* 4 Enterkin Burn: early Namurian marine mudstone */

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4 Enterkin Burn: early Namurian marine mudstone

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	The valley side comprises a scarp of weathered basalt lava flows resting on poorly exposed Coal Measures. The base of the Coal Measures is best seen on the SE bank of the Enterkin Burn (NS 8726 0542) where it is marked by a coarse-grained sandstone with quartz pebbles. This lies unconformably on about 2.5 m of sandstone, which rests on fossiliferous mudstone (Simpson and Richey, 1936). The beds below the unconformity belong to the Enterkin Mudstone Formation, which is exposed in several places in the Enterkin Burn. This formation consists of a thin, gently dipping sequence of purplish red sandstone and seatearth interbedded with deep purple-red, fossiliferous siltstone and mudstone. On biostratigraphical grounds, these strata could be as young as early Namurian, although a Brigantian age is also possible. A few metres downstream, sandstone underlying the fossiliferous beds rests unconformably upon steeply dipping Ordovician greywacke turbidites and shales.		The valley side comprises a scarp of weathered basalt lava flows resting on poorly exposed Coal Measures. The base of the Coal Measures is best seen on the SE bank of the Enterkin Burn (NS 8726 0542) where it is marked by a coarse-grained sandstone with quartz pebbles. This lies unconformably on about 2.5 m of sandstone, which rests on fossiliferous mudstone (Simpson and Richey, 1936). The beds below the unconformity belong to the Enterkin Mudstone Formation, which is exposed in several places in the Enterkin Burn. This formation consists of a thin, gently dipping sequence of purplish red sandstone and seatearth interbedded with deep purple-red, fossiliferous siltstone and mudstone. On biostratigraphical grounds, these strata could be as young as early Namurian, although a Brigantian age is also possible. A few metres downstream, sandstone underlying the fossiliferous beds rests unconformably upon steeply dipping Ordovician greywacke turbidites and shales.

	The fossiliferous Enterkin Mudstone Formation beds contain a rich and varied fauna (Brand, 1990) including: ~~brachiopods: ''Buxtonia ''sp., ''Composita ''sp., latissimoid productoids, ''Pleuropugnoides ''sp., ''Productus ''sp., ''Pugilis ''sp., ''Retispira decussata''~~		The fossiliferous Enterkin Mudstone Formation beds contain a rich and varied fauna (Brand, 1990) including:

	bivalves: ''Aviculopecten ''cf. ''interstitialis, Edmondia ''sp., ''Leiopteria ''cf. ''thompsoni, Limipecten ''sp., ''Parallelodon ''cf. ''semicostatus, Pernopecten ''sp., ''~~Polidevci a~~ attenuata, Schizodus?, Wilkingia? ''Nautiloids, orthocones and trilobite pygidia have also been found.		brachiopods: ''Buxtonia ''sp., ''Composita ''sp., latissimoid productoids, ''Pleuropugnoides ''sp., ''Productus ''sp., ''Pugilis ''sp., ''Retispira decussata''

			bivalves: ''Aviculopecten ''cf. ''interstitialis, Edmondia ''sp., ''Leiopteria ''cf. ''thompsoni, Limipecten ''sp., ''Parallelodon ''cf. ''semicostatus, Pernopecten ''sp., ''Polidevcia attenuata, Schizodus?, Wilkingia? ''Nautiloids, orthocones and trilobite pygidia have also been found.

	Aspects of the fauna are common to the north margin of the Thornhill Basin and the Sanquhar Basin to the north (Davies, 1970), suggesting that in the late Carboniferous the marine influence of the Midland Valley was being felt as far south as Thornhill.		Aspects of the fauna are common to the north margin of the Thornhill Basin and the Sanquhar Basin to the north (Davies, 1970), suggesting that in the late Carboniferous the marine influence of the Midland Valley was being felt as far south as Thornhill.