This is a mainly car-based expedition to examine various features in this beautiful dale. We drive straight to Fulhope to sample the limited exposures of Cheviot rhyolite. The geological survey classifies the rock as ‘mica-felsite’. It is a purplish rock with white feldspar phenocrysts. There is little evidence of mica to the naked eye. In the dry stone walls it has a rather more crinkly texture than the commoner andesite.
We then drive to Blindburn to view the excellent exposures of blocky andesite resting on a bed of tuff and ignimbrite on the opposite (South) side of the Coquet. We drive past the traditional hay meadows of Barrowburn, and notice that the Wood Cranesbill is in flower beside the road.
We stop at Bygate to try to locate the Acklington Dyke in the river bed. We find it in a rather inaccessible spot in the river. The Dyke has nothing to do with either the Devonian Cheviot volcanics or the Permian Whin Sill. It is one of a series of tholeiitic dolerite dykes radiating from the Eocene Mull volcano, and reaching right on to the Northumberland coastal plain.
Our final port of call is Kateshaw Crag at the roadside between Bygate and Shillmoor. The andesite here has weathered to produce beautiful blue-green phenocrysts of chlorite. We were trying to find the quartz-porphyry dyke which has been mapped in the river bed here. We could see a bed of rock on the opposite bank which looked more granitic than the surrounding andesite but the river was too deep to wade so confirmation eluded us.ACKLINGTON DYKEANDESITEBLINDBURNBYGATESCHLORITECOQUETFELDSPARFULHOPEIGNIMBRITEKATESHAW CRAGMICA-FELSITEPHENOCRYSTSQUARTZ-PORPHYRYRHYOLITETHEOLIITIC BASALTTUFFWOOD CRANESBILL
Tag Archives: tuff
Knock Hill and Upper Linhope Burn
Knock Hill (NT 99584 16499) with its attendant gorge is an impressive feature on the road towards Linhope. It is composed of ignimbrite, and gives evidence that the Cheviot volcanic system was explosive, and produced abundant pyroclastic surges and ash fall, as well as andesite lava flows.
The 1” OS geological map notes a ‘hypersthene-porphyrite’ dyke which we locate at NT 99584 16499 on the south side of the Breamish burn, just beyond the road bridge.
From here, a walk to the upper reaches of the Linhope Burn (around NT 94094 17459) and on to the Standrop Burn. (NT 93794 17839) There is a dacite dyke showing in the streambed just above the two burns’ confluence.
The streambed reveals a variety of rock types. The coarse-grained (Standrop) and finer-grained pink (Dunmoor) varieties in evidence. There is also a much finer grained pale rock similar to the ‘evolved’ granophyre from the Cheviot.
According to Al-Hafdh, this is ‘Woolhope’ granite, part of a ring dyke that circles from the upper Standrop Burn area through to the upper Dunmoor Burn area.