Editing Cheviot — early Devonian volcanic rocks, granite and basement - an excursion

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In the waterfall just downstream of the houses and in exposures upstream is volcanic breccia. The rock consists of matrix-supported angular to subangular clasts, mostly of green andesite up to several tens of cm in diameter. The matrix is greenish grey, fine grained and full of small, irregular shaped, chlorite-filled '''amygdales'''. Rock the same as the matrix occurs alternating with exposures of deep purple andesite downstream to the junction with Gable Burn [NT 8342 1105]. Units of breccia and finer-grained tuffs occur throughout the andesite pile. They have not been studied in recent years. At Blindburn the textures visible in outcrop suggest the rock might be a '''pyroclastic''' flow breccia rather than an air-fall deposit.
 
In the waterfall just downstream of the houses and in exposures upstream is volcanic breccia. The rock consists of matrix-supported angular to subangular clasts, mostly of green andesite up to several tens of cm in diameter. The matrix is greenish grey, fine grained and full of small, irregular shaped, chlorite-filled '''amygdales'''. Rock the same as the matrix occurs alternating with exposures of deep purple andesite downstream to the junction with Gable Burn [NT 8342 1105]. Units of breccia and finer-grained tuffs occur throughout the andesite pile. They have not been studied in recent years. At Blindburn the textures visible in outcrop suggest the rock might be a '''pyroclastic''' flow breccia rather than an air-fall deposit.
  
==== Locality 7 [NT 8919 0649], at Linbriggs, is the best of the many exposures of andesite in the river ====
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==== Locality 7 [NT 8919 0649], at Linbriggs, is the best of the many exposures of andesite in the river ====
  
Park near the farm buildings and start with the roadside exposure on the east side, about 30 m south of the bridge. At the southern end of the exposure is massive, purplish grey porphyritic andesite, which passes northwards into finely brecciated, amygdaloidal rock marking the top of the flow. Above and to the north is a second flow of rubbly andesite. This rock is purplish brown and highly amygdaloidal with epidote and chlorite-filled irregular vesicles. Blocks and 'pillows' are set in hydrothermally altered, rotted andesite, but the flow has a core of massive rock some 6 m long and 2.5 m high. In the gorge, upstream of the bridge, the general southerly dip to the pile of flows is clearly seen. Good, polished exposures of amygdaloidal and flow-banded andesite are present in the river bed.
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Park near the farm buildings and start with the roadside exposure on the east side, about 30 m south of the bridge. At the southern end of the exposure is massive, purplish grey porphyritic andesite, which passes northwards into finely brecciated, amygdaloidal rock marking the top of the flow. Above and to the north is a second flow of rubbly andesite. This rock is purplish brown and highly amygdaloidal with epidote and chlorite-filled irregular vesicles. Blocks and 'pillows' are set in hydrothermally altered, rotted andesite, but the flow has a core of massive rock some 6 m long and 2.5 m high. In the gorge, upstream of the bridge, the general southerly dip to the pile of flows is clearly seen. Good, polished exposures of amygdaloidal and flow-banded andesite are present in the river bed.
  
==== Locally 8 [NT 9040 0648] is a cattle grid 1.5 km beyond Alwinton ====
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==== Locally 8 [NT 9040 0648] is a cattle grid 1.5 km beyond Alwinton ====
  
The southern boundary of the Cheviot Volcanic Group is faulted. The road from here to Linbriggs is close to and parallel to the fault. Small craggy exposures in the steep hillside on the north of the road are andesite. On the southern side of the Coquet valley, on Barrow Scar, subhorizontal, well-bedded Carboniferous rocks are clearly visible ([[Lower Carboniferous at Bowden Doors, Roddam Dene and the Coquet Gorge - an excursion|Excursion 9]]). Note at the eastern end of the exposure the prominent upper limestone bed has sagged as a result of landslipping. The fault can be positioned to within a metre in the stream running down to the road here from the north. Here, about 50 m from the road, a small exposure of sandstone is a metre from andesite.
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The southern boundary of the Cheviot Volcanic Group is faulted. The road from here to Linbriggs is close to and parallel to the fault. Small craggy exposures in the steep hillside on the north of the road are andesite. On the southern side of the Coquet valley, on Barrow Scar, subhorizontal, well-bedded Carboniferous rocks are clearly visible ([[Lower Carboniferous at Bowden Doors, Roddam Dene and the Coquet Gorge - an excursion|Excursion 9]]). Note at the eastern end of the exposure the prominent upper limestone bed has sagged as a result of landslipping. The fault can be positioned to within a metre in the stream running down to the road here from the north. Here, about 50 m from the road, a small exposure of sandstone is a metre from andesite.
  
  

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