On the Occurrence of Agmatite in the Rogart Migmatite Area, Sutherland: A Study in Granitization

Abstract

Agmatite was one of the new descriptive terms introduced by the late Professor J. J. Sederholm in connection with his life-long study of the Finnish migmatites. He applied this name to a group of migmatites which present an appearance that has suggested the terms “eruptive breccia” and”intrusion breccia”, but agmatite has a very different genesis from that connoted by these terms. Sederholm (1923, p. 117) wrote: “As these migmatites consisting of fragments of older rocks cemented by granite are genetically and petrologically very different from many of the rocks that have been called eruptive breccias many of which are volcanic rocks, the author proposes to designate this group of migmatites as agmatites (from ἂγμα, fragment).” The elaborate drawings and illustrations to be found in Sederholm's Memoirs (1923, 1926), however, give a much clearer idea of the appearance presented by these rocks than any written description.