The Acid Rocks of Western Rhum

Abstract

In the west of the Isle of Rhum (Inverness-shire), Tertiary acid rocks outcrop over an area of approximately 6 square miles. A core of spherulitic microgranite is surrounded by graphpphyre1 which, in turn, is bounded on the north by Torridonian Sandstone; although much of the boundary is marked by a low-angle reverse fault, part of the junction is undisturbed and a belt of transitional rocks, some 1,400 feet in width, intervenes between the graphophyre and the Torridonian Sandstone. The transitional rocks are divisible into five zones which are interpreted as marking successive stages in the conversion of sandstone into graphophyre. Evidence is presented indicating that the microgranite, into which the graphophyre grades inwards, represents a still more advanced stage of transformation.