The Migmatite Area Around Bettyhill, Sutherland

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Abstract
Summary The Migmatization of pelitic, semipelitic, siliceous and hornblendic (Durcha type) rocks of the Moine Series is a record of a lengthy series of metasomatic changes brought about by the activity of alkaline solutions. Pelitic gneisses are converted by soda-metasomatism into permeation-gneisses. Semipelitic granulites give rise to augen-migmatites through the action of potash-bearing fluids. Siliceous and hornblendic rocks are relatively resistant to change. Various types of granite-gneisses arise from the different sedimentary parents. Many sheets of pegmatite, granite and aplite are shown by their field relations to have been formed by the gradual metasomatism of the country rocks, probably by the long-continued passage of fluids along certain channels. I. Introduction The area which forms the subject of this paper is about l0 square miles in extent and forms a narrow strip along the north coast of Sutherland, from the River Naver eastwards to near Kirktomy. This small region provides excellent examples of the migmatization of the various lithological types of the Moine Series and its associated intrusions. It consists of numerous small injection zones varying greatly both in width and length, most of them being roughly parallel to the regional foliation. Though the beds are affected by small faults and thrusts, their strike is sufficiently persistent and the lithological characters of comparatively thin layers are sufficiently constant to permit the tracing in the field of the changes in a number of zones in response to different degrees of migmatization. It has thus been possible to prove beyond reasonable doubt the