Editing Carboniferous rocks of the Roman Wall and Haltwhistle Burn - an excursion

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==== Locality 2 ====
 
==== Locality 2 ====
  
Make a short detour at Twice Brewed [NY 751 668], turning north to Steel Rigg. From the car park just north of the wall [NY 751 677], walk 100 m from the southeast corner along the wall to the edge of the '''overflow channel''' and a superb view of the Whin escarpment, with its columnar '''jointing''', and Crag Lough in the middle distance ([[:File:YGS_NORTROCK_FIG_11_2.jpg|Figure 11.2]]).
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Make a short detour at Twice Brewed [NY 751 668], turning north to Steel Rigg. From the car park just north of the wall [NY 751 677], walk loo m from the southeast corner along the wall to the edge of the overflow channel and a superb view of the Whin escarpment, with its columnar jointing, and Crag Lough in the middle distance ([[:File:YGS_NORTROCK_FIG_11_2.jpg|Figure 11.2]]).
  
Return to the Military Road, which over the next 2 km west has the dip slop of the Whin continuing on the north side but to the south the features are buried under till. They gradually emerge near the junction at NY 730 663 where quarries in the Four Fathom Limestone can be seen alongside the road and in the Great Limestone near the skyline; these features strengthen and the Four Fathom Limestone crosses the road at [NY 720 662]. To the south quarries and lime kilns indicate the position of the Great Limestone with further quarries in the sandstone above it.
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Return to the Military Road, which over the next 2 km west has the dip slop of the Whin continuing on the north side but to the south the features are buried under till. They gradually emerge near the junction at NY 730663 where quarries in the Four Fathom Limestone can be seen alongside the road and in the Great Limestone near the skyline; these features strengthen and the Four Fathom Limestone crosses the road at [NY 720 662]. To the south quarries and lime kilns indicate the position of the Great Limestone with further quarries in the sandstone above it.
  
Turn north at the Milecastle Inn [NY 716 660] to Cawfields. Immediately on the right is a good section of the Four Fathom Limestone exposed in an old quarry, while on a raised hillock on the left, between the road and Haltwhistle Burn, is the site of the fortlet that guarded this section of the Stanegate. Between the Four Fathom Limestone and the top surface of the Whin are the remains of old workings in coal below the Three Yard Limestone and '''siderite''' ironstone bands in shales in the same part of the succession. The most striking feature, however, is the vallum and mounds running along the base of the Whin feature. Continue to Cawfields quarry car park.
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Turn north at the Milecastle Inn [NY 716 660] to Cawfields. Immediately on the right is a good section of the Four Fathom Limestone exposed in an old quarry, while on a raised hillock on the left, between the road and Haltwhistle Burn, is the site of the fortlet that guarded this section of the Stanegate. Between the Four Fathom Limestone and the top surface of the Whin are the remains of old workings in coal below the Three Yard Limestone and siderite ironstone bands in shales in the same part of the succession. The most striking feature, however, is the vallum and mounds running along the base of the Whin feature. Continue to Cawfields quarry car park.
  
==== Locality 3, Cawfields Quarry [NY 713 666] ====
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==== Locality 3, Cawfields Quarry [NY 713 666] ====
  
The car park and lake are on the site of the old whinstone quarry which removed not only the scarp of the Sill but also the Roman Wall that ran along its top; working ceased when they approached Milecastle 42 and the break in the continuity of the escarpment.
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The car park and lake are on the site of the old whinstone quarry which removed not only the scarp of the Sill but also the Roman Wall that ran along its top; working ceased when they approached Milecastle 42 and the break in the continuity of the escarpment.
  
The top surface of the Sill defines the land surface; a thin skin of '''metamorphosed''' sediment can be found in places. Columnar jointing is developed perpendicular to the top, cooling surface, of the intrusion. In the old quarry walls on the south side of the car park the fine grained chilled margin of the sill can be seen, but is very thin. More obvious is the band of vesicles 2 m below the top. These formed by gas, released from the magma by reduced pressure as it rose towards the surface. Their presence at a definite level in the sill suggests that the magma close to the surface contact had cooled to a viscosity that prevented the bubbles rising any further, most of the vesicles have later been filled with '''calcite'''.
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The top surface of the Sill defines the land surface; a thin skin of metamorphosed sediment can be found in places. Columnar jointing is developed perpendicular to the top, cooling surface, of the intrusion. In the old quarry walls on the south side of the car park the fine grained chilled margin of the sill can be seen, but is very thin. More obvious is the band of vesicles 2 m below the top. These formed by gas, released from the magma by reduced pressure as it rose towards the surface. Their presence at a definite level in the sill suggests that the magma close to the surface contact had cooled to a viscosity that prevented the bubbles rising any further, most of the vesicles have later been filled with calcite.
  
Along the north side of the lake, a stile over the low stone wall permits access to the main quarry face, which at its northern end exposes the base of the sill, resting on sandstone dipping southwest at 45°. To the east, behind the quarry face, the Whin escarpment is offset along the line of a small northwest–southeast valley. The valley may mark the position of a fault, '''downthrowing''' east, displacing the Whin escarpment to the north. Recent geophysical work, however, suggests that the displacement is due to a transgression of the sill and it seems probable that both faulting and transgression are involved. On the east side of the small valley Milecastle 42 occupies a sloping site and has short stubs of broad wall on either side joining on to the narrower linking wall section.
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Along the north side of the lake, a stile over the low stone wall permits access to the main quarry face, which at its northern end exposes the base of the sill, resting on sandstone dipping southwest at 45°. To the east, behind the quarry face, the Whin escarpment is offset along the line of a small northwest–southeast valley. The valley may mark the position of a fault, downthrowing east, displacing the Whin escarpment to the north. Recent geophysical work, however, suggests that the displacement is due to a transgression of the sill and it seems probable that both faulting and transgression are involved. On the east side of the small valley Milecastle 42 occupies a sloping site and has short stubs of broad wall on either side joining on to the narrower linking wall section.
  
 
If time permits, the walk westwards from Cawfields via the fort of ''Aesica ''to Walltown, largely on the Whin dip slope, is very rewarding archaeologically.
 
If time permits, the walk westwards from Cawfields via the fort of ''Aesica ''to Walltown, largely on the Whin dip slope, is very rewarding archaeologically.
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=== Haltwhistle Burn ===
 
=== Haltwhistle Burn ===
  
As well as a good dip section through the Carboniferous succession, Haltwhistle Burn provides an insight into the rich industrial heritage of the area ([[:File:YGS_NORTROCK_FIG_11_3.jpg|Figure 11.3]]). The Whin quarry at Cawfields was linked by a narrow gauge railway, down the burn to Haltwhistle and the main Newcastle-Carlisle railway. Other industrial activities in the vicinity were mining of ironstone from below the Three Yard Limestone, probably smelted at Haltwhistle; mining of coal from three separate seams; quarrying of the Great and Four Fathom Limestones, burnt in lime kilns for agricultural lime and mortar; quarrying of sandstone for building; mining of '''fireclay''' for bricks, pots and pipes; quarrying of '''ganister''' for firebricks for furnace linings; and the working of '''galena''' for lead and silver.
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As well as a good dip section through the Carboniferous succession, Haltwhistle Burn provides an insight into the rich industrial heritage of the area ([[:File:YGS_NORTROCK_FIG_11_3.jpg|Figure 11.3]]). The Whin quarry at Cawfields was linked by a narrow gauge railway, down the burn to Haltwhistle and the main Newcastle-Carlisle railway. Other industrial activities in the vicinity were mining of ironstone from below the Three Yard Limestone, probably smelted at Haltwhistle; mining of coal from three separate seams; quarrying of the Great and Four Fathom Limestones, burnt in lime kilns for agricultural lime and mortar; quarrying of sandstone for building; mining of fireclay for bricks, pots and pipes; quarrying of ganister for firebricks for furnace linings; and the working of galena for lead and silver.
  
==== Locality 4 Approach the burn from the white gate just west of the cottage on the south side of the Military Road [NY 714 659] ====
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==== Locality 4 Approach the burn from the white gate just west of the cottage on the south side of the Military Road [NY 714 659] ====
  
The Four Fathom Limestone is exposed in the stream bed under the road bridge but can only be reached from the south side of the burn. The track down Haltwhistle Burn, mostly the old railway line, is well marked. From the gate, the field surface is the top of the sandstone between the Four Fathom and Great Limestones and it can be seen outcropping in places through the thin soil. At the stream the upper half of the Great Limestone is exposed, about 7 m thick, in well defined '''posts''' with clay partings; the bedding is disturbed by a small fault crossing just upstream. Further exposures are present in the stream bed but nowhere is the full thickness of the limestone exposed. Overlying the limestone are the Tumbler Beds, calcareous shale with thin bands of limestone, so called because they often show small scale '''folding.''' On the east side of the burn the shale fragments provide a rich fauna of small '''brachiopods, crinoid''' ossicles and calyx plates, '''echinoid''' plates, '''corals''' and '''bryozoa'''.
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The Four Fathom Limestone is exposed in the stream bed under the road bridge but can only be reached from the south side of the burn. The track down Haltwhistle Burn, mostly the old railway line, is well marked. From the gate, the field surface is the top of the sandstone between the Four Fathom and Great Limestones and it can be seen outcropping in places through the thin soil. At the stream the upper half of the Great Limestone is exposed, about 7 m thick, in well defined posts with clay partings; the bedding is disturbed by a small fault crossing just upstream. Further exposures are present in the stream bed but nowhere is the full thickness of the limestone exposed. Overlying the limestone are the Tumbler Beds, calcareous shale with thin bands of limestone, so called because they often show small scale folding. On the east side of the burn the shale fragments provide a rich fauna of small brachiopods, crinoid ossicles and calyx plates, echinoid plates, corals and bryozoa.
  
Downstream, beyond lime kilns on both banks, the basal section of the sandstone above the Great Limestone is exposed in the east bank. It is thin bedded and shows fine detail of sedimentary structures picked out by severe wind erosion in its exposed position. Around the next bend are the remains of the colliery which worked the Little Limestone Coal; the chimney and engine block are still standing. Fragments of the coal can be found and the overlying Little Limestone, rich in bryozoa, is exposed in the hillside behind the chimney; there is a smaller exposure downstream in the west bank. The Little Limestone is rarely exposed, since it is only 3–4 m thick.
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Downstream, beyond lime kilns on both banks, the basal section of the sandstone above the Great Limestone is exposed in the east bank. It is thin bedded and shows fine detail of sedimentary structures picked out by severe wind erosion in its exposed position. Around the next bend are the remains of the colliery which worked the Little Limestone Coal; the chimney and engine block are still standing. Fragments of the coal can be found and the overlying Little Limestone, rich in bryozoa, is exposed in the hillside behind the chimney; there is a smaller exposure downstream in the west bank. The Little Limestone is rarely exposed, since it is only 3–4 m thick.
  
==== Locality 5 [NY 709 655] ====
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==== Locality 5 [NY 709 655] ====
  
 
Cross to the west bank by the footbridge. South dipping interbedded massive sandstones and shales are exposed in the banks, with two of numerous quarries in the sandstones adjacent to the footbridge. Apparent changes in the dip of the sandstones downstream, particularly well seen at Jackdaw Crags where the massive sandstone in the east bank, underlain by a thin coal, appears to be synclinal, are due to the frequent changes in stream direction. The dip is constant. Stream erosion across the shale/ sandstone alternations has produced a very sinuous course.
 
Cross to the west bank by the footbridge. South dipping interbedded massive sandstones and shales are exposed in the banks, with two of numerous quarries in the sandstones adjacent to the footbridge. Apparent changes in the dip of the sandstones downstream, particularly well seen at Jackdaw Crags where the massive sandstone in the east bank, underlain by a thin coal, appears to be synclinal, are due to the frequent changes in stream direction. The dip is constant. Stream erosion across the shale/ sandstone alternations has produced a very sinuous course.
  
==== Locality 6 [NY 707 651] ====
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==== Locality 6 [NY 707 651] ====
  
In Leeshall Quarry, on the west bank, two sandstones are separated by a 25 cm coal, the same as that at the base of Jackdaw Crags, underlain by '''seatearth''' 2 m thick. The sequence reflects the build up of the Carboniferous delta top to water level allowing the growth of plants and the formation of peat. Downstream of Leeshall Quarry the path returns to the east bank via the old railway bridge in which the narrow gauge tracks are still embedded. Continue downstream to the picnic place where an excellent dipping top bedding surface of the Upper Leeshall Quarry Sandstone can be seen in the stream. Stay close to the edge of the stream where the Oakwood Limestone crops out just above water level on the west bank. The exposure continues for 20 m downstream to just above the wooden footbridge. The 2–3 m thick limestone is impure with a high clay content and is a significant marker horizon in this part of the succession dominated by sandstone and shale.
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In Leeshall Quarry, on the west bank, two sandstones are separated by a 25 cm coal, the same as that at the base of Jackdaw Crags, underlain by seatearth 2 m thick. The sequence reflects the build up of the Carboniferous delta top to water level allowing the growth of plants and the formation of peat. Downstream of Leeshall Quarry the path returns to the east bank via the old railway bridge in which the narrow gauge tracks are still embedded. Continue downstream to the picnic place where an excellent dipping top bedding surface of the Upper Leeshall Quarry Sandstone can be seen in the stream. Stay close to the edge of the stream where the Oakwood Limestone crops out just above water level on the west bank. The exposure continues for 20 m downstream to just above the wooden footbridge. The 2–3 m thick limestone is impure with a high clay content and is a significant marker horizon in this part of the succession dominated by sandstone and shale.
  
==== Locality 7 [NY 708 649] ====
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==== Locality 7 [NY 708 649] ====
  
 
Downstream on the east bank, sandstone, underlain by the shale above the Oakwood Limestone, forms the main face of a large quarry, set back from and running parallel to the burn. Nearby are the remains of another colliery, a drift into the base of the cliff marked by some stone packing and a concrete tunnel from which issues a flow of water, white with alum. The colliery initially worked a thin coal above the Oakwood Limestone but later it mainly mined fireclay for the pottery, recently closed, a few metres ahead. The remains of the kilns and the large sandstone wheels used to grind up the clay are still in the yard and glazed pipes can be found.
 
Downstream on the east bank, sandstone, underlain by the shale above the Oakwood Limestone, forms the main face of a large quarry, set back from and running parallel to the burn. Nearby are the remains of another colliery, a drift into the base of the cliff marked by some stone packing and a concrete tunnel from which issues a flow of water, white with alum. The colliery initially worked a thin coal above the Oakwood Limestone but later it mainly mined fireclay for the pottery, recently closed, a few metres ahead. The remains of the kilns and the large sandstone wheels used to grind up the clay are still in the yard and glazed pipes can be found.
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{{EWwalks}}
 
{{EWwalks}}
  
[[Category:Northumbrian rocks and landscape: a field guide ]]
 
 
[[Category:7. Northern England]]
 
[[Category:7. Northern England]]

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