Excursion 7: Laig Gorge and Clach Alasdair (Route map 4)

This excursion conveniently combines a visit to the Laig Gorge, which is the best locality on Eigg for the oyster-bearing part of the Jurassic succession, and also for Cretaceous conglomerate, sandstone, and limestone, with an opportunity to collect ammonites and belemnites from the south shore of Laig Bay. The gorge itself is wet, slippery, and a favourite haunt of midges, and the shore also lacks non-geological attractions, but the walk is pleasant and the views excellent.

From Glebe Barn or the eastern part of the island, follow the road and the forestry track as described in Excursion 1. Descend the bluff along the path, admiring the kettle-hole lochan to your right, but instead of continuing to Laig Farm, skirt the lochan and make for the gorge made by the stream Abhainn a’ Cham Loin, known as Laig Gorge to geologists.

Laig Gorge

Scramble past brambles and briars into the gorge [NM 47259 87522]. The lowest beds seen are oyster-bearing limestones of the Duntulm Formation. Above them, also in the lower gorge, are fine-grained muddy limestones of the Kilmaluag Formation. There are many fallen blocks of the Cretaceous Laig Gorge Sandstone Member of the Strathaird Limestone Formation, including its basal conglomerate. On the north bank of the stream there is a rounded outcrop of quartz porphyry. Scramble up it (not recommended in wet weather) into the upper gorge, where there are good exposures of the Laig Gorge Sandstone and Strathaird Limestone, overlain by basalt. The limestone is fine grained and does not contain fossils visible to the naked eye but microfossils seen in thin section enable its dating. It does not contain flints. For details, see the Geological Survey memoir, pp. 31–36.

Clach Alasdair

From the gorge walk to Laig Farm and thence head westwards above the stony shore. A low tide is needed here. Where patches of grey mudstone appear among the boulders, examine them and search for ammonites, especially Cardioceras, belemnites and bivalves (page 13). The hillside above shows landslip topography where basalt has slipped seaward over the soft and easily eroded mudstone. At Clach Alasdair, the basalts extend to sea level. Between the basalt and the Jurassic mudstone is a hard bed of Cretaceous age, less than a metre thick, bearing large flints reminiscent of those in the English Chalk. It is very different from the Laig Gorge limestone, and rests on younger Jurassic strata, demonstrating that much erosion occurred between Late Jurassic and Late Cretaceous times. Return by the track from Laig Farm to Cuagach.