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GRANITE AND GREYWACKE

Just above the granite junction on Redstone Rig

The granite of the Galloway Highlands melted its way up into the standard Southern Upland rock, which is the chunky deep-ocean sandstone called greywacke. Around the edges of the granite the country rock is cooked and crumbled, so all around Mullwarchar and Craignaw lie valleys such as the Silver Flowe. But a mile or two further out, the surrounding greywacke was baked and hardened, and this tougher rock rises in the hill ridges of Merrick and the Kells and Minnigaffs. The result is a ‘metamorphic areole’, also known as 50 miles of fine hill-walking in a ring around the granite heartland.

The difference between the Merrick’s greywacke and the granite around Loch Enoch is fairly noticeable as you descend Redstone Rig. Dark, uniform grey gives way to paler speckles; layered sandstone gives way to rounded granite. To inspect the actual rock junction, take a leftward line down the ridge and look for a striking slab sloped towards you. The granite–greywacke junction crosses the downhill rockface below (NX 4343 8532).