Downward-facing structures of the Highland Border

Abstract

Summary The structures in the Dalradian rocks near the Highland Border of Scotland consistently face downwards. They are upside-down. In the south-western districts they face downwards to the south-east, between Loch Lomond and Aberfoyle vertically downwards and from Aberfoyle to Stonehaven downwards towards the north-west. The view that the Upper Dalradian Ben Ledi Grits and Leny Grits are equivalent and younger than the Aberfoyle Slates which outcrop between them is tentatively supported. The Aberfoyle anticline implied by this view must face downwards, not upwards as previously claimed. The downward-facing structures are connected with the recumbent folds to the north-west. The Carrick Castle anticline, formerly regarded as the hinge at the front of the Loch Tay inversion, is thought not to exist. That hinge is either located in the Aberfoyle anticline, which would thus mark the southern limit of the Loch Tay inversion, or, if the Aberfoyle anticline does not exist, the hinge lies in the Ben Ledi Grits. On either view the roots of the Highland Border structures lie north of the Loch Tay flat belt. The steep zone of down turned and overturned nappes near the Highland Border represents a powerful monocline associated with the Highland Boundary fault. It connects the Grampian Highlands with the Midland Valley. The nappes possibly continue beneath the Midland Valley.