XXI. The Igneous Rocks of Bute

Abstract

The geological claims of Bute seem always to have been overshadowed by the near presence of Arran, with its superior size and variety of formations. MacCulloch, in his “Geology of the Western Islands” (1819, p. 445), devotes some space to emphasising the importance of Bute geologically, and then dismisses the island in twenty-nine pages. Bryce, in his “Geology of Arran and the other Clyde Islands” (1872), reproaches MacCulloch for his injustice, and then generously allows Bute three pages more, or thirty-two pages, as against 315 pages devoted to Arran. The object of the work recorded in the present paper has been to continue and amplify the work recorded in the Geological Survey Memoir (1903) as far as it relates to the igneous rocks of Bute. The igneous rocks in the area have been mapped and studied with the aid of numerous thin sections under the microscope. The lavas of Calciferous Sandstone age will be described in the light of recent classification, certain occurrences of rocks hitherto unknown in the district will be recorded, while in some cases evidence will be advanced which may necessitate change in the interpretation of rocks already described. Distribution of the Igneous Rocks. The Island of Bute is divided into approximately equal halves by the Highland Boundary Fault which crosses the island from Rothesay Bay to Scalpsie Bay. The northern half is composed of Highland schists, grits, and phyllites, and the igneous rocks are confined to a few dykes and the Scalpsie epidiorite This 250-word extract was created in the absence of an abstract