Our objective is to examine the different types of ‘granite’ on the uplands above the Hawsen Burn and in the upper reaches of the College Valley around Goldscleugh where the northern ‘granite’ meets the andesite. On the climb up past Hawsen Crags we have an excellent view of a pair of stonechats. The torrential rain of November and December 2015 has gouged out a ditch by the path to a depth of at least a metre (NT93932 23084). In this gulley we find plenty of breccia which may perhaps be bedrock. One piece in particular consists of rather fine banded agate which has obviously been formed before brecciation and then cemented together again with more silica. This may be evidence for the location of one of the elusive volcanic vents.
The summit plateau before descending to Goldscleugh offers splendid views of the upper College Valley. The terrain is peat bog, and what few rocks appear are of the pink porphyritic type, some coarser, some finer grained. We descend to the Lambden Burn. Ian explores along the streambed in an easterly direction, and confirms the geological survey that tongues of ‘granite’ penetrate the andesite on the north side of the burn.
We stop to examine the rocks at the southerly branch of the head of the Lambden Burn. Ian discovers an outcrop (NT 92655 22523) which closely resembles the Evolved granular granite on the upper slopes of Cheviot. We contemplate the nearby Woolhope Crag but decide to leave that for another expedition.
As we return down the Hawsen Burn, Ian branches off to examine the Hawsen Crag (NT 94797 23216).
Tag Archives: Hawsen Burn
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.