Another example is the decline of species that build calciferous shells, attributed to ocean acidification caused by carbon dioxide dissolving in the seas.

The Carboniferous rocks of the Cumbrae belong to the lower part of the Calciferous Sandstone series with the accompanying volcanic zone.

The Carboniferous rocks include, at the base, the Calciferous Sandstone series of dark shales with thin limestones, sandstones and coals.