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Ballagan Beds in Auchenreoch Glen

Ballagan Beds is the name given to certain sedimentary deposits laid down during the early Carboniferous period. Compare NY3881 : Ballagan Formation.

As explained by John Mitchell in the book "Loch Lomondside" (New Naturalist Series, 2001), they comprise "some 180 metres of alternating beds of cementstones and thin-bedded silty mudstones. Whereas the mudstones are derived from material washed down from the high ground during rainy seasons, the cementstones are impure limestones precipitated during extended periods of drought".

This photograph shows a detail from the steep, bare southern side of lower NS4178 : Auchenreoch Glen (see that item for the context of the present photograph). The stratification is clearly evident here, as it is throughout most of the glen. The wall of rock shown here is made up of layers of crumbly, fractured shale (the mudstone), interleaved with layers containing paler, rounded nodules (of cementstone).

The layers of shale are fragile; poking at the rockface often brings some material down. Many of the cementstone nodules, after having eroded out of the wall of rock, can be seen lying in the bed of the burn; they often have quite distinctive surface patterns. For just one example of many, see NS4178 : Cementstone nodule in Auchenreoch Glen.