Introduction. The coast immediately southward from Ayr, including the striking and picturesque double headland of the Heads of Ayr, has attracted little attention from geologists. It is briefly mentioned in the old Survey memoir upon the district by Sir A. Geikie (1869),1 who later gave a few facts regarding the volcanic vents of the coast in his Ancient Volcanoes of Great Britain (1897). W. Burns had previously contributed a short discursive paper to these Transactions (1888). The fullest account is contained in a newspaper article by the late R. Boyle describing, in a popular style, the geology of the coast from Ayr to Dunure (1908). Much the same ground had been covered by J. Smith (1895) in a short paper which made a brief mention of the Greenan—Heads of Ayr shore. The same author has also contributed a brief note on the globular shale of the Deil’s Dyke to these Transactions (1898). An examination of the coast had long been projected, because the magnificent vertical and horizontal sections exhibited in the Heads of Ayr, of one of the Carboniferous volcanic vents so common in Scotland, seemed to promise much information regarding the mechanism of this type of vent. Unfortunately the sections, good as they are, were disappointing in this respect; but their examination, along with that of other igneous phenomena of this stretch of coast, has yielded a quantity of interesting data, which are presented in this paper. General Geology .—The coast consists of gently rolling strata of the Cementstone Group This 250-word extract was created in the absence of an abstract