Tag Archives: Hedgehope Hill

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The Hawsen Burn

We find plenty of fine-grained granophyric rock but we are not convinced that it really is of the same type as the ‘Evolved’ rock from the summit and north slopes of the Cheviot. Subsequent thin section analysis suggests that it and samples from the Standrop Burn are rather different from the ‘Evolved’ type. However, the Hawsen Burn samples do share the high quartz and low plagioclase content of the ‘Evolved’ rock of the Upper Cheviot area. At any rate, we now feel that there is insufficient evidence to argue that the fine-grained granophyric rocks are all part of a common ring dyke system. They are quite likely to be separate intrusions, some of them representing very late magmatic activity.
We locate a medium-grained but rather altered, pink porphyritic variety at NT 94299 23027 which seems to correspond with varieties found on Dunmoor and Hedgehope Hills.
There is plenty of evidence of altered andesite, hornfelsed by contact with the pluton as we would expect here as the Hawsen Burn runs along the boundary between the two in some places.

Altered yellowish andesite at NT 94504 23011 is stated in some guides to contain massive epidote but there was none in the samples that we thinned.

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Dunmoor Hill

We make a return visit to Dunmoor Hill. The summit tors of the hill present a medium-grained pink granitic rock that look very similar to that of the summit of Hedgehope Hill.
Long Crag (not the same as Long Crags, near Housey Crag in the Harthope valley) reveals a very similar rock. Al-Hafdh classifies the former as ‘Hedgehope granodiorite’ and the latter as ‘Dunmoor granodiorite’. Actually, both in hand specimen and thin section, they are very similar in appearance and mineral content – an observation born out by Al-Hafdh’s own chemical analysis of the types.
We remain unconvinced that they can be separated into two types belonging to separate intrusions.
Al-Hafdh argues that the two are separated by a belt of coarse porphyritic granodiorite (‘Standrop’ variety). A tor containing the coarse rock certainly appears at NT 96890 17969 about half way between the summit and Long Crag, but the extent of peat bog over the hill precludes any way of establishing whether this is part of a wider belt separating the summit of Dunmoor Hill from Long Crag.
A further descent down the south side of the hill reveals again the junction between the pink medium grained porphyritic rock ‘(Dunmoor’/’Hedgehope’) and the dioritic ‘Marginal’ variety.
Cat Crag is definitely composed of the ‘Marginal’ variety.
We look for the hornfelsed andesite that geological map locate close to Long Crag, but we don’t find it.

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Hedgehope Hill

A visit to Hedgehope Hill confirms that the upper Dunmoor Burn contains a very fine-grained granophyric rock. We have provisionally classified this as ‘Evolved’ granite but have since become increasingly doubtful whether it is really part of the same intrusion as the evolved granophyre on the upper slopes of the Cheviot, and whether it really does form part of a ring dyke as Al-Hafdh suggested. Exposure is too limited in the upper Dunmoor Burn to draw definite conclusions.
About 100m below the summit of Hedgehope Hill, the track crosses a large boulder field which is probably the result of periglacial activity. The great majority of these boulders belong to the coarse porphyritic type which Al-Hafdh named ‘Standrop granodiorite’. The summit of Hedgehope has a medium to fine-grained pink rock which is similar to that of Dunmoor Hill. Many samples from the summit show evidence of significant hydrothermal alteration.
Returning via the north side of Hedgehope Hill towards the Harthope valley, we find more of the coarse-grained ‘Standrop’ rock but, after much searching, fail to find the chilled margin between the finer and coarser varieties that Al-Hafdh says is visible there. The one example of really fine-grained rock chilled against the courser rock turns out to be another felsite or aplite dyke.