Editing The Quaternary of South Tynedale - an excursion

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=== Locality 8 [NY 740 418] ===
 
=== Locality 8 [NY 740 418] ===
  
Walk northwestwards through the village along the minor road on the western side of the South Tyne. At the point where the Pennine Way leaves the road to follow the river towards Alston is a footbridge over the South Tyne. From the bridge can be seen a series of low alluvial terraces. They have been studied in detail by Aspinall et al. (1986). The lowest and youngest of the terraces (terrace 3 on [[:File:YGS_NORTROCK_FIG_12_3.jpg|Figure 12.3]]) is considered by them to be a direct consequence of excess floodplain and channel bed aggradation during the main lead-mining period, followed by later incision. Sediment, predominantly fines, was derived from the erosion of riverbank waste dumps, etc. These and other metalliferous river terraces, together with the modern floodplain, are the main habitat of a suite of heavy-metal tolerant plant species ('metallophytes') — which otherwise occur on mine dumps — and include ''Minuartia verna ''(spring sandwort) and ''Thlaspi caerulescens ''(alpine penny-cress), both of which are abundant on the floodplain here. [[:File:YGS_NORTROCK_FIG_12_3.jpg|Figure 12.3]] shows the terraces, and also migration of the river channel over the floodplain during the last 130 years, the information being derived from successive Ordance Survey maps. The three terraces above the present floodplain are clearly visible on the ground, with the higher terraces exhibiting palaeobars and channels. Very low concentrations of heavy metals occur in the higher terraces (terraces 1 and 2), which are between 3 and 6 m above the river. However concentrations are much higher on the lowest right bank terrace (terrace 3), 2 m above the river, and on the floodplain itself. The latter (from the first O.S. map) existed by 1859. The highest concentrations of lead, copper, zinc and cadmium were in fact found in the 1859 river bed, when lead production was at its peak. Clearly the lowest terrace and the present floodplain date from the lead-mining period (eighteenth and nineteenth centuries) and subsequently, while terraces 1 and 2 predate this mining activity but are otherwise of unknown (presumed Flandrian) age. All of these low terraces (1, 2 and 3) post-date the higher one on which Garrigill village is situated.
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Walk northwestwards through the village along the minor road on the western side of the South Tyne. At the point where the Pennine Way leaves the road to follow the river towards Alston is a footbridge over the South Tyne. From the bridge can be seen a series of low alluvial terraces. They have been studied in detail by Aspinall ''et al. (1986). ''The lowest and youngest of the terraces (terrace 3 on [[:File:YGS_NORTROCK_FIG_12_3.jpg|Figure 12.3]]) is considered by them to be a direct consequence of excess floodplain and channel bed aggradation during the main lead-mining period, followed by later incision. Sediment, predominantly fines, was derived from the erosion of riverbank waste dumps, etc. These and other metalliferous river terraces, together with the modern floodplain, are the main habitat of a suite of heavy-metal tolerant plant species ('metallophytes') — which otherwise occur on mine dumps — and include ''Minuartia verna ''(spring sandwort) and ''Thlaspi caerulescens ''(alpine penny-cress), both of which are abundant on the floodplain here. [[:File:YGS_NORTROCK_FIG_12_3.jpg|Figure 12.3]] shows the terraces, and also migration of the river channel over the floodplain during the last 130 years, the information being derived from successive Ordance Survey maps. The three terraces above the present floodplain are clearly visible on the ground, with the higher terraces exhibiting palaeobars and channels. Very low concentrations of heavy metals occur in the higher terraces (terraces 1 and 2), which are between 3 and 6 m above the river. However concentrations are much higher on the lowest right bank terrace (terrace 3), 2 m above the river, and on the floodplain itself. The latter (from the first O.S. map) existed by 1859. The highest concentrations of lead, copper, zinc and cadmium were in fact found in the 1859 river bed, when lead production was at its peak. Clearly the lowest terrace and the present floodplain date from the lead-mining period (eighteenth and nineteenth centuries) and subsequently, while terraces 1 and 2 predate this mining activity but are otherwise of unknown (presumed Flandrian) age. All of these low terraces (1, 2 and 3) post-date the higher one on which Garrigill village is situated.
  
Garrigill is a starting point for climbing Cross Fell, and should anyone be tempted it is worth noting that the Pennine Way route to the summit passes near to the Bullman Hills (NY 7037) and the Lambgreen Hills [NY 711 364]. These hills are giant glacial erratics: slabs of the Great Limestone which have been rafted up to 1 km from original outcrop. The larger giant erratics are capped by till and this by blanket peat. ( '''To climb Cross Fell it is necessary to be properly equipped for fell-walking.)'''
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Garrigill is a starting point for climbing Cross Fell, and should anyone be tempted it is worth noting that the Pennine Way route to the summit passes near to the Bullman Hills (NY 7037) and the Lambgreen Hills [NY 711 364]. These hills are giant glacial erratics: slabs of the Great Limestone which have been rafted up to 1 km from original outcrop. The larger giant erratics are capped by till and this by blanket peat. ( ''To climb Cross Fell it is necessary to be properly equipped for fell-walking.)''
  
 
Return to Hexham either by the same route, or via Nenthead and Allendale (noting asymmetry in all of the dales).
 
Return to Hexham either by the same route, or via Nenthead and Allendale (noting asymmetry in all of the dales).

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