Metamorphism and migmatisation in the Ythan Valley, Aberdeenshire

Old and new information is collated concerning the progressive metamorphic and migmatitic series from slate through knotted phyllite, andalusite-cordierite-schist, cordierite-sillimanite-gneiss to permeation-gneiss and finally migmatitic gneiss developed in the Ythan Valley. This series, the result of regional thermal metamorphism culminating in migmatisation, constitutes the Buchan Type of plutonic series. It differs from the classic Barrovian metamorphic zones and the Cromar Type of migmatite developed in regions farther south in that temperature control is dominant and so-called antistress minerals have a regional distribution.