Peniel Heugh is a popular place to visit primarily for the impressive 45m (150 ft) Waterloo monument that was erected between 1817 and 1824 to commemorate the Battle of Waterloo and for the spectacular views over the Border Region afforded even from the base of the monument. The 237 m (791 ft) hill is also the site of a Iron Age settlement.
Walks are described from the nearby Harestanes Visitor Centre but we parked in a space by one of the tracks on the western side of the hill on the small road that heads north to Maxton from the B6400 that heads east from Ancrum to Nisbet.
Map showing sample locations and rock types around Peniel Heugh
The microgabbro. that was intruded as a volcanic plug at Peniel Heugh has, like the microgabbro at Dunion Hill, a tendency towards a trachytic texture in which plagioclase crystals are similarly oriented along lines of flow. However, in the samples that we collected at Peniel Heugh, we see a larger gain size than we see in the Dunion hill rock as well as a greater number of augite phenocrysts. This difference may be actual or merely apparent as a consequence of our (under) sampling.
The distribution of minerals in the rock viewed in thin section with crossed polarising filters (FoV 16 x 10 mm)
Location 1. South-western outcrop of the intrusion
Prepared specimen viewed in ordinary reflected light (measures 42mm across)
Section viewed in plane polarised light (FoV 4.6 x 3.0 mm)
Plagioclase, pyroxene, chlorite, magnetite with a few long crystals of apatite in the Peniel Heugh microgabbro. Section viewed with crossed polarising filters (FoV 2.3 x 1.5 mm)
Location 2. Outcrops on the western side of the intrusion below the monument
Prepared specimen viewed in ordinary reflected light (measures 45mm across)
Section viewed in plane polarised light (FoV 4.6 x 3.0 mm)
Section viewed with crossed polarising filters (FoV 2.3 x 1.5 mm)
Section viewed in plane polarised light (FoV 2.3 x 1.5 mm)
Section viewed in plane polarised light (FoV 1.2 x 0.8 mm)
Location 3. Quarry to the west of the monument
This may have been the source for the microgabbro element of the Waterloo monument
Prepared specimen viewed in ordinary reflected light (measures 42mm across)
References
MacAdam A.D., Clarkson E.N.K., Stone, P. (editors) 1993 Scottish Borders geology: an excursion guide.Edinburgh, Scottish Academic Press.
BGS online Geology of Britain http://mapapps.bgs.ac.uk/geologyofbritain/home.html