Bellyside Crag and Upper Goldscleugh Sike

We buy a 10.00 GBP day permit from Savills, Glendale Road, Wooler and drive up the College Valley to Dunsdale where we start our walk up Bellyside Hill. The purpose of the expedition is to examine the granitic rock at the northern end of the pluton at Bellyside Crag which is classified by Al-Hafdh and by previous writers as ‘Marginal’ like the rock of Cunyon Crag and Dunmoor Hill on the south east side of the pluton. We also hope to find and examine the andesite outlier mapped at the head of Goldscleugh to see if it gives any clues as to its relationship with the pluton.

Bellyside Hill

View from Bellyside Hill looking up towards Goldscleugh Sike
The ground behind is the summit plateau of the Cheviot.

Bellyside Hill is Cheviot’s closest approximation to a classic ridge walk. Until about 600m there is a good path passing a series of granitic tors on the way. These are composed of a granitic but in appearance mafic rock with occasional felsic intrusions of pink rock.
At about 600m the path disappears and the only way forward is through tiresome blanket bog vegetation.

View looking north down Bellyside Hill showing the outcropping tors

View looking north down Bellyside Hill showing the outcropping tors

View looking north down Bellyside Hill showing the outcropping tors

A felsic phase or dyke in one of the tors on Bellyside Hill

Upper Goldscleugh reveals some rather heavily altered rock which may possibly be andesite, but it occurs as scattered blocks and pebbles, so it is impossible to determine any relationship with the pluton. If it is indeed andesite, its altered state indicates that it must have originated from close to the pluton contact.

We now tramp over to Bellyside Crag. This turns out to be composed of a mafic granitic rock similar to that found on the tors of Bellyside Hill.
The screes around the crag have a large colony of clubmosses.

Thin section of rock from Bellyside Crag viewed with crossed polars at X40

Thin section of rock from Bellyside Crag viewed with crossed polars at X40
Granophyric texture can be seen in several places. There is a large crystal of clinopyroxene at the bottom of the picture.

Subsequent thin section analysis reveals some interesting facts. The rocks of Bellyside Hill and Bellyside Crag are very similar to each other although the Bellyside Hill specimens may have a slightly higher proportion of alkali feldspar. However, neither are anything like the ‘Marginal’ rock of Dunmoor Hill and Cunyon Crag.
The Bellyside Hill specimens have a lower proportion of plagioclase to alkali feldspar (identifiable feldspars show a ratio of about 1:2, plagioclase to alkali feldspar); there is very little biotite, the main mafic mineral being pyroxene (10-15%); quartz content is similar at about 20%. It also has a more marked fine matrix than the southern Marginal with frequent granophyric texture.
It therefore seems rather doubtful that it has the same origin as the southern Marginal rock.

As regards the “andesite” of upper Goldscleugh Sike, if we are correct in identifying this as a granite/andesite contact, both the andesite and granite show clear signs of banding which may indicate contact compression.
Apart from the contact on Shiel Cleugh Edge, this is the only evidence for kinematic action which we have found on Cheviot. Where it exists it appears to be very localised. However, we remain rather uncertain whether the rock from upper Goldscleugh Sike was andesite or just an altered granitic rock.