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

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The first exposure is pink '''microgranite''' about 300 m up. A further 50 m beyond, a very small exposure in the stream shows a sharp contact between pink microgranite and dark purplish grey porphyritic andesite. This illustrates the nature of this contact, which is a complex series of dykes and veins of microgranite penetrating the andesite.
 
The first exposure is pink '''microgranite''' about 300 m up. A further 50 m beyond, a very small exposure in the stream shows a sharp contact between pink microgranite and dark purplish grey porphyritic andesite. This illustrates the nature of this contact, which is a complex series of dykes and veins of microgranite penetrating the andesite.
  
==== Locality 5 [NT 9501 2281] is 10 m beyond the first tributary coming in from the north ====
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==== Locality 5 [NT 9501 2281] is 10 m beyond the first tributary coming in from the north ====
  
An exposure of andesite shows many features of contact metamorphism — close '''joints''', splintery when struck, small dark spots in the groundmass. Upstream from here exposures of microgranite and andesite alternate.
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An exposure of andesite shows many features of contact metamorphism — close joints, splintery when struck, small dark spots in the groundmass. Upstream from here exposures of microgranite and andesite alternate.
  
==== Locality 6 [NT 9473 2296] is about 200 m below a circular, stone sheep fold ====
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==== Locality 6 [NT 9473 2296] is about 200 m below a circular, stone sheep fold ====
  
A big boulder of '''quartz''' with '''haematite''' stringers is in the stream adjacent to a breccia separating microgranite from rotted and quartz veined andesite. Veinlets of black tourmaline are in the microgranite. This locality marks the site of a west-northwest fault that is roughly coincident with the granite boundary.
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A big boulder of quartz with haematite stringers is in the stream adjacent to a breccia separating microgranite from rotted and quartz veined andesite. Veinlets of black tourmaline are in the microgranite. This locality marks the site of a west-northwest fault that is roughly coincident with the granite boundary.
  
==== Locality 7 [NT 9456 2302] is about 50 m below the sheepfold ====
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==== Locality 7 [NT 9456 2302] is about 50 m below the sheepfold ====
  
A denuded patch of hillside, 3 m high, immediately above the stream is deeply hydrothermally altered, rotten andesite with 3 cm thick veins and stringers of tourmaline and lumps of massive epidote. This altered rock continues upstream adjacent to a crush zone first seen 100 m beyond the sheep fold. Two crush zones intersect here. A wall of breccia trending east–west stands at the foot of a steep slope which consists of crushed andesite up to 2 m wide with north–south quartz veins. Tourmaline, crystalline quartz, haematite and '''limonite''' are abundant. These crush zones are common in the Cheviots and are always associated with hydrothermal alteration.
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A denuded patch of hillside, 3 m high, immediately above the stream is deeply hydrothermally altered, rotten andesite with 3 cm thick veins and stringers of tourmaline and lumps of massive epidote. This altered rock continues upstream adjacent to a crush zone first seen too m beyond the sheep fold. Two crush zones intersect here. A wall of breccia trending east–west stands at the foot of a steep slope which consists of crushed andesite up to 2 m wide with north–south quartz veins. Tourmaline, crystalline quartz, haematite and limonite are abundant. These crush zones are common in the Cheviots and are always associated with hydrothermal alteration.
  
Climb up to the footpath to return to the road. From there, the prominent Hausey and Long Crags on the east side of the Harthope valley to the southeast are roof pendants of '''hornfelsed''' volcanic rocks resting on granite. These, and a roof pendant of volcanic rocks actually on The Cheviot show that the exposed granite is the roof zone of the intrusion.
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Climb up to the footpath to return to the road. From there, the prominent Hausey and Long Crags on the east side of the Harthope valley to the southeast are roof pendants of hornfelsed volcanic rocks resting on granite. These, and a roof pendant of volcanic rocks actually on The Cheviot show that the exposed granite is the roof zone of the intrusion.
  
 
Walk along the road to Langleeford, then the track on the north side of the burn.
 
Walk along the road to Langleeford, then the track on the north side of the burn.

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