VII.— Notes on the Geological Structure of South Bute

Abstract

Introduction Following the pioneer work of Gunn (1903) for the Geological Survey, W. R. Smellie made a detailed investigation of the southern part of the island and published his results in two valuable papers in our Transactions (1915, 1916). These papers deal chiefly with the Calciferous Sandstone lavas, necks and intrusions, and with the two great sills, or sheets as they will be called here, which run right across the south end. The latter consist of: (a) the Tertiary composite intrusion made up of three sheets of dolerite (one central, two marginal) and two sheets of quartz-oligoclase-porphyry (above and below the central dolerite); and (b) a crinanite sheet which Smellie assigned to the Permo-Carboniferous. The present writer, however, follows H. J. W. Brown (1931) in believing that the crinanite is also of Tertiary age. Smellie has published two maps of the area containing the inclined sheets. As these two maps are somewhat different from one another reference will only be made to the later (1916, pl. xxxix, six inches to one mile) unless specially indicated. During a month’s stay at Kilchattan the writer re-mapped large areas in the southern part of the island with results which are different in certain respects from Smellie’s. Summary of Geology Practically the whole of South Bute consists of Calciferous Sandstone lavas. The underlying Upper Old Red Sandstone outcrops along the north-east coast and at Dunagoil Bay, with an outcrop on the south-west side of each of two important N.W.–S.E. faults (a) at Glen Callum This 250-word extract was created in the absence of an abstract