Editing Middle and Upper Carboniferous rocks (Millstone Grit and Coal Measures) of the Sheffield region - an excursion

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Excursion 10b (Westphalian, Coal Measures) is a disused quarry at Bradgate Brickyard [SK 413 935] near Rotherham, northeast of Sheffield, requiring 1–2 hrs. Take the A6109 from Sheffield to approximately 300 m north of the junction with the A629. Parking is limited to minor roads to the west of the quarry and coaches are advised to find parking elsewhere.
 
Excursion 10b (Westphalian, Coal Measures) is a disused quarry at Bradgate Brickyard [SK 413 935] near Rotherham, northeast of Sheffield, requiring 1–2 hrs. Take the A6109 from Sheffield to approximately 300 m north of the junction with the A629. Parking is limited to minor roads to the west of the quarry and coaches are advised to find parking elsewhere.
  
''Note: ''Parties wishing to visit Bradgate Brickyard (lob) should first seek permission from Swift & Co.
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''Note: ''Parties wishing to visit Bradgate Brickyard (lob) should first seek permission from Swift & Co., 56 Birley Moor Road, Sheffield, S12 4W (tel: 0114 265 1023)
  
 
'''''Hammering is forbidden''' ''on Burbage Edge (Excursion 10a).
 
'''''Hammering is forbidden''' ''on Burbage Edge (Excursion 10a).
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==== Locality 2 [S[SK 268 815] ====
 
==== Locality 2 [S[SK 268 815] ====
  
After about 1 km the prominent scarp becomes less well-defined. Just to the south the scarp becomes much more prominent again but is some 400 m to the east of the path. This abrupt change in position is due to a fault '''downthrowing''' to the north. However, to the west, of the prominent flat-topped hills Carl Wark (see Locality 5) and Higger Tor (see Locality 6), Higger Tor to the right (north) is over 45 m higher, indicating its relative upward displacement. A further 500 m along the footpath to the southwest, a large quarry is visible in the scarp to the east. Leave the path and ascend to this quarry, taking care as you go through the boulder field below the quarry entrance.
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After about 1 km the prominent scarp becomes less well-defined. Just to the south the scarp becomes much more prominent again but is some 400 m to the east of the path. This abrupt change in position is due to a fault downthrowing to the north. However, to the west, of the prominent flat-topped hills Carl Wark (see Locality 5) and Higger Tor (see Locality 6), Higger Tor to the right (north) is over 45 m higher, indicating its relative upward displacement. A further 500 m along the footpath to the southwest, a large quarry is visible in the scarp to the east. Leave the path and ascend to this quarry, taking care as you go through the boulder field below the quarry entrance.
  
 
==== Locality 3 (SK 266 810] ====
 
==== Locality 3 (SK 266 810] ====
  
The Rivelin Grit here has been extensively quarried and the 20 m high, vertical joint faces (popular among climbers) show large foreset beds dipping towards the south. Numerous millstones, in various stages of completion, lie around the quarry entrance; some are up to 1.9 m across and nearly 0.4 m thick. Also visible in the adjacent scarp to the south of the quarry are boreholes showing the method of extraction of the sandstone blocks. Follow the quarry path obliquely across the boulder field to the southwest and pass through the old stone gate posts along the track to the quarry approximately 60 m from the junction with the main footpath. There is a fine example of a stone trough (difficult to locate when the bracken is high), and yet more millstones, just before the junction with the main path. Take the minor track at [SK 262 808] to the northwest, towards Burbage Brook, where there are small exposures of shales which underlie both leaves of the Rivelin Grit.
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The Rivelin Grit here has been extensively quarried and the 20 m high, vertical joint faces (popular among climbers) show large foreset beds dipping towards the south. Numerous millstones, in various stages of completion, lie around the quarry entrance; some are up to 1.9 m across and nearly 0.4 m thick. Also visible in the adjacent scarp to the south of the quarry are boreholes showing the method of extraction of the sandstone blocks. Follow the quarry path obliquely across the boulder field to the southwest and pass through the old stone gate posts along the track to the quarry approximately 60 m from the junction with the main footpath. There is a fine example of a stone trough (difficult to locate when the bracken is high), and yet more millstones, just before the junction with the main path. Take the minor track at [SK 262 808] to the northwest, towards Burbage Brook, where there are small exposures of shales which underlie both leaves of the Rivelin Grit.
  
 
==== Locality 4 [SK 262 809] ====
 
==== Locality 4 [SK 262 809] ====
  
A larger exposure occurs on the west bank 75 m further north (access via the west bank). Here, fissile dark-grey shales along a track in a north-northwest direction.
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A larger exposure occurs on the west bank 75 m further north (access via the west bank). Here, fissile dark-grey shales along a track in a north-northwest direction.
  
 
==== Locality 5 [SK 260 814] ====
 
==== Locality 5 [SK 260 814] ====
  
At Carl Wark the Rivelin Grit may be examined and palaeocurrent directions determined. A few millstones may be seen among the boulders on the eastern slopes of the hill. Carl Wark (Earl Wark on old maps) is the site of an Iron Age Fortification (2500–2000 years old) and on the western side of the hill a 7 m wide earth rampart and a 2 m high stone wall form impressive reminders of the fort. A former entrance and stone trough (Iron Age or Roman) can also be seen and an information plaque is located near the entrance. The footpath route then continues in a north-northwest direction to Higger Tor.
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At Carl Wark the Rivelin Grit may be examined and palaeocurrent directions determined. A few millstones may be seen among the boulders on the eastern slopes of the hill. Carl Wark (Earl Wark on old maps) is the site of an Iron Age Fortification (2500–2000 years old) and on the western side of the hill a 7 m wide earth rampart and a 2 m high stone wall form impressive reminders of the fort. A former entrance and stone trough (Iron Age or Roman) can also be seen and an information plaque is located near the entrance. The footpath route then continues in a north-northwest direction to Higger Tor.
  
 
==== Locality 6 [SK 806 819] ====
 
==== Locality 6 [SK 806 819] ====
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From Higger Tor there are splendid views of Burbage Edge, Carl Wark and the form of the Burbage inlier, as well as further scarp edges of the Rivelin Grit at Over Owler Top towards the south-southwest. Note the pebbly nature of the grit and various scales of cross-bedding. The direction of transport may be measured and compared to that at the previous localities.
 
From Higger Tor there are splendid views of Burbage Edge, Carl Wark and the form of the Burbage inlier, as well as further scarp edges of the Rivelin Grit at Over Owler Top towards the south-southwest. Note the pebbly nature of the grit and various scales of cross-bedding. The direction of transport may be measured and compared to that at the previous localities.
  
The quickest way back to the car park and Locality 8 is to drop down to the road on the footpath, over steps recently constructed to combat erosion, and then turn right. However, if time permits, an additional locality may be visited at Callow Bank where the lower leaf of the Rivelin Grit is exposed. From Locality 6, cross the road after having descended from Higger Tor and take the footpath opposite. After about 40 m another path is reached; turn left and continue for some 100 m before branching off to the right and follow the contours to the prominent scarp and landslip area of Callow Bank.
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The quickest way back to the car park and Locality 8 is to drop down to the road on the footpath, over steps recently constructed to combat erosion, and then turn right. However, if time permits, an additional locality may be visited at Callow Bank where the lower leaf of the Rivelin Grit is exposed. From Locality 6, cross the road after having descended from Higger Tor and take the footpath opposite. After about 40 m another path is reached; turn left and continue for some too m before branching off to the right and follow the contours to the prominent scarp and landslip area of Callow Bank.
  
 
==== Locality 7 [SK 252 823] ====
 
==== Locality 7 [SK 252 823] ====
  
At Callow Bank 0–15 m of dark grey shales, with occasional flat, tabular '''sideritic''' nodules and rare plant fragments, crop out below the lower leaf of the Rivelin Grit. The shales, which have yielded rare specimens of ''Gastrioceras ''crop out ''in situ ''as well as forming part of a slumped area (recognized by the hummocky ground) below the crags of the Rivelin Grit. Continue examining the shale outcrops up the slope towards the crags and note that they coarsen slightly until, just below the grit, the shales are interbedded with thin cross-laminated siltstone and fine sandstones. The lower leaf of the Rivelin Grit rests with a sharp junction (scoured surface) on the interbedded siltstones and sandstones. The grit is formed of apparently massive sandstones, but careful observation will reveal the presence of diffuse bedding and interbedded siltstone horizons. Further up the slope a poorly exposed interval indicates the presence of a finer-grained unit before further thick sandstones are exposed at the top of the slope. To reach Locality 8 at Upper Burbage Brook, return to the road and continue in a northerly direction (passing the car park) until Upper Burbage Bridge is reached. Descend to the exposures between the road and the confluence of the two streams.
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At Callow Bank 0–15 m of dark grey shales, with occasional flat, tabular sideritic nodules and rare plant fragments, crop out below the lower leaf of the Rivelin Grit. The shales, which have yielded rare specimens of ''Gastrioceras ''crop out ''in situ ''as well as forming part of a slumped area (recognized by the hummocky ground) below the crags of the Rivelin Grit. Continue examining the shale outcrops up the slope towards the crags and note that they coarsen slightly until, just below the grit, the shales are interbedded with thin cross-laminated siltstone and fine sandstones. The lower leaf of the Rivelin Grit rests with a sharp junction (scoured surface) on the interbedded siltstones and sandstones. The grit is formed of apparently massive sandstones, but careful observation will reveal the presence ofdiffuse bedding and interbedded siltstone horizons. Further up the slope a poorly exposed interval indicates the presence of a finer-grained unit before further thick sandstones are exposed at the top of the slope. To reach Locality 8 at Upper Burbage Brook, return to the road and continue in a northerly direction (passing the car park) until Upper Burbage Bridge is reached. Descend to the exposures between the road and the confluence of the two streams.
  
 
==== Locality 8 [SK 261 829] ====
 
==== Locality 8 [SK 261 829] ====
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The quarry is located to the right of the road at the top of a grassy bank, just after crossing over the roundabout with the junction of the A629. The quarry face may be in variable states of degradation but most of the features described below should be exposed. The gentle northeast dip ([[:File:YGS_YORKROCK_FIG_10_03B.jpg|Figure 10.3b]]) is clearly visible, as is the range of rock types that make up typical Coal Measure cycles. Shales and mudstones with ironstone nodules, in which comminuted plant debris is locally abundant, dominate the sequence. Thin coal seams, seatearths and variably developed siltstones and fine-grained sandstones also occur. The mudrocks are dominantly non-marine but show evidence of occasional marine incursions; the siltstones and sandstones are the result of mainly fluvial activity, while the coals and seatearths indicate plant colonization during periods of emergence.
 
The quarry is located to the right of the road at the top of a grassy bank, just after crossing over the roundabout with the junction of the A629. The quarry face may be in variable states of degradation but most of the features described below should be exposed. The gentle northeast dip ([[:File:YGS_YORKROCK_FIG_10_03B.jpg|Figure 10.3b]]) is clearly visible, as is the range of rock types that make up typical Coal Measure cycles. Shales and mudstones with ironstone nodules, in which comminuted plant debris is locally abundant, dominate the sequence. Thin coal seams, seatearths and variably developed siltstones and fine-grained sandstones also occur. The mudrocks are dominantly non-marine but show evidence of occasional marine incursions; the siltstones and sandstones are the result of mainly fluvial activity, while the coals and seatearths indicate plant colonization during periods of emergence.
  
Point '''A''' (not shown on [[:File:YGS_YORKROCK_FIG_10_03A.jpg|Figure 10.3a]], [[:File:YGS_YORKROCK_FIG_10_03B.jpg|Figure 10.3b]]) is the level of the Joan Coal and overlying shales; these are usually obscured by scree. The Joan Coal lies approximately 14 m below the sandstone bed at '''B'''. The dark grey shales immediately above the coal have yielded the inarticulate '''brachiopod''' ''Lingula ''(horizon equivalent to Clay Cross Marine Band in this area). The geological features within the 15 m of strata exposed in the quarry may be followed on the log ([[:File:YGS_YORKROCK_FIG_10_03A.jpg|Figure 10.3a]]) with reference to the five prominent beds or units '''B–F'''. Point '''G''' (not shown on [[:File:YGS_YORKROCK_FIG_10_03A.jpg|Figure 10.3a]], [[:File:YGS_YORKROCK_FIG_10_03B.jpg|Figure 10.3b]]) is the level of the Lidgett Coal (rarely exposed) which occurs approximately 5.5 m above the top of the sandstones at '''F'''. Thin coal seams are present between the sandstones at '''F''' and the Lidgett Coal.
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Point A (not shown on [[:File:YGS_YORKROCK_FIG_10_03A.jpg|Figure 10.3a]], [[:File:YGS_YORKROCK_FIG_10_03B.jpg|Figure 10.3b]]) is the level of the Joan Coal and overlying shales; these are usually obscured by scree. The Joan Coal lies approximately 14 m below the sandstone bed at B. The dark grey shales immediately above the coal have yielded the inarticulate brachiopod ''Lingula ''(horizon equivalent to Clay Cross Marine Band in this area). The geological features within the 15 m of strata exposed in the quarry may be followed on the log ([[:File:YGS_YORKROCK_FIG_10_03A.jpg|Figure 10.3a]]) with reference to the five prominent beds or units B–F. Point G (not shown on [[:File:YGS_YORKROCK_FIG_10_03A.jpg|Figure 10.3a]], [[:File:YGS_YORKROCK_FIG_10_03B.jpg|Figure 10.3b]]) is the level of the Lidgett Coal (rarely exposed) which occurs approximately 5.5 m above the top of the sandstones at F. Thin coal seams are present between the sandstones at F and the Lidgett Coal.
  
 
Please keep any disturbance of the rock face to a minimum.
 
Please keep any disturbance of the rock face to a minimum.

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