Geology
The Highland Boundary Fault reflects a major geological change where hard metamorphic rocks in the north joined with pebble conglomerates and softer sandstones to the south. The crunch zone is called the Highland Boundary complex, marked today by the Mentieth Hills. The zone is over 1km wide and includes a sequence of lavas, conglomerates, limestones, black mudstones and sandstones. The fault extends out to Arran in the west not far from this massive slab of sandstone.
410 million years ago
The harder rocks to the north were deposited and then altered and crumpled by heat and pressure to form the highlands. The hills are dominated by metamorphic rocks such as schist, slate and quartzite. The oldest rock in the world is Lewisian Gneiss, formed 3,000 million years ago and found in the Outer Hebrides.
800 million years ago
Basaltic lava flows and volcanic ashes erupt from fissures and small volcanic cones in the Campsie Fells and Gargunnock Hills. The flows are the bold ‘scarp’ features on the north face of these hills and the eroded roots of the volcanoes form isolated hills like Dumgoyne. Stirling Castle sits on a slab of volcanic rock forced up from a distant volcanic fissure.
340 million years ago
Between a rock and a hard place
