XXIV. The Classification of the Post-Carboniferous Intrusive Igneous Rocks of the West of Scotland

Abstract

I. Introduction. No one studying the geological maps of Scotland, on whatever scale, can fail to be impressed by the enormous amount of igneous activity they disclose in the geological history of that country. The broad areas of pink or brown, indicating great lava plateaux, and the splashes and stripes of crimson, indicating intrusive rocks, are literally everywhere. Not only are the igneous rocks widely distributed in space, but also in time. Practically every formation up to the Permian supplies its quota. In the Archaean we have the great foundation of gneiss, with its inextricable tangle of acid and basic igneous rocks. The Dalradian schists and gneisses of the Grampians are everywhere penetrated by igneous masses now largely metamorphosed to massive epidiorites and hornblende schists. The Cambrian of the north-west Highlands contains an interesting complex of highly alkaline rocks, including borolanite and several other rare types. The Ordovician, Devonian, Carboniferous, and Permian in Scotland each exhibit a great series of extrusive and intrusive igneous rocks. Finally, after a long period of quiescence in the Mesozoic, an enormous outburst of igneous activity in the Tertiary gave rise to the great lava plateaux of the Western Isles. This richness in material makes Scotland a petrographer's paradise. The amount of work that has been done, however, in spite of the labours of Zirkel, Allport, Judd, Geikie, Teall, Harker and others, is very little in comparison with the great amount that still remains for petrographers to do. “No adequate investigation,” This 250-word extract was created in the absence of an abstract