Time and tide wait for no man and truth is often stranger than fiction. Both these sayings apply to Scotland, especially Argyll with its islands at ‘the edge of the world’. Here, historic stones – some truly associated with destiny, others more dubiously linked by legend – fascinate and abound.
Coll and Tiree, to the northwest of Mull and Iona, are non-identical ‘twins’. Coll is rugged and rocky; Tiree is low, fertile and flat. However, in common with islands of the Outer Hebrides, both have pure white strands of calcareous sand made chiefly from maerl, backed by sand dunes of flower strewn machair (a low-lying grassy plain found on some of the northwest coastlines of Ireland and Scotland, in particular, the Outer Hebrides). Individually, they have their own strange, legendary stones – glacial erratics that have drawn myth to themselves and one which ‘rings’ its own warning today.
Maerl is formed when Atlantic Ocean currents force upwards dissolved mineral that nourishes the marine organisms of the Hebridean fringe. From this rich cold water, calcium carbonate is extracted, not only by invertebrates to make their shells, but also by the calcareous red algae, Phymatolithon and Lithothamnion coralloides, collectively known as ‘maerl’. Found at depths of between 10 and 18m, living maerl beds produce small granules between 2 and 10mm in size that accumulate in beds and which grow at 1mm a year. Sorted by currents and eventually washed landwards where they are tumbled by Atlantic waves into sand, the resulting white beaches are continuously resupplied with new deposits on the western shores. Westerly winds constantly blow this fine sand inland, forming high dunes, which, when colonised by a specific flora, are destined to become the Hebrides own unique machair.