The plateau type was most extensively developed during the formation of the Calciferous Sandstone; the puy type was of somewhat later date.
The thin seams of the Calciferous Sandstone are not workable, but the bituminous shales in the Firth of Forth basin are largely worked for the manufacture of mineral oil.
There was great volcanic activity during the deposition of the Calciferous Sandstone, Carboniferous Limestone and Millstone Grit series.
The mineral is chiefly obtained from seams in the Calciferous Sandstone at the base of the Carboniferous rocks.
The Carboniferous rocks of Arran include representatives of the Calciferous Sandstone, the three subdivisions of the Carboniferous Limestone series, and to a small extent the Coal Measures, and are confined to the north part of the island.