White trap in some Ayrshire Coals

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Abstract
Synopsis: Small intrusions of basic igneous rock in certain coals in the West Ayrshire coalfield occur as discrete bodies of white trap. In the Sillyhole Coal near Dalmellington these bodies are either horizontally elongated varying in shape from lenticular to nearly spherical, or small, vertically elongated and of more irregular shape. The coal is altered to vesicular natural coke with polygonal jointing, the axes of the coke polygons being curved so as to be normal both to the margins of the seam and to the junction with the white trap. The combined thickness of the seam of coal and white trap is always greater than the thickness of the same seam in an unaltered state, the total thickness being directly proportional to the amount of white trap present in the seam. Coals containing white trap bodies of this type passed through a plastic phase when magma was being intruded. During this period the horizontally elongated white trap bodies were formed, their mode of formation being analogous to that of pillow lavas. With rising temperature the coal re-solidified and shrank to form coke polygons, the magma filling joints between polygons and locally expanding to form the vertically elongated white trap bodies.

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