Geology of the Aberfoyle district: Palaeogene basalts and dolerites

This topic provides a summary of the geology of the Aberfoyle district – covered by the British Geological Survey. 1:50k geological map sheet 38E (Scotland). Authors: C W Thomas, A M Aitken, E A Pickett, J R Mendum, E K Hyslop, M G Petterson, D Ball, E Burt, B Chacksfield, N Golledge and G Tanner (BGS).

The youngest dykes observed in the region are rare feldspar-phyric basalts and dolerites. These form part of the regional north-west-trending Palaeogene dyke swarm of western Scotland. Palaeogene dykes are not recorded in the district north of the Highland Boundary Fault Zone. Where they occur south of the fault they have north-westerly trends. The best example is the large dyke that crops out over Fir Hill [NS 538 969], on the south side of Loch Ard Forest. This dyke is approximately 15 m wide and can be traced for over 3 km, appearing to bifurcate at its north-west end.