Observations on the Tiree Marble, with Notes on others from Iona

Abstract

I. Introduction. Although so well known, and represented in many mineralogical collections, the Tiree Marble has never been described in detail. Macculloch says that the Tiree flesh-coloured marble ‘resembles the greater number of the primary limestones found in gneiss and mica-slate, and may be considered as a large nodule ... The nodule of limestone ... appears to be an irregular mass of about 100 feet in diameter, and is surrounded on all sides by gneiss.’ [The marble] ‘occasionally contains imbedded lumps of granite or gneiss, similar to those which occur in the limestone of Glen Tilt. These are always visible at the surface, from their superior power of resisting the action of the atmosphere.’ He also describes the exposures of limestone in a field south-east of Balephetrish Hill. He says that ‘it is possible that the masses of limestone thus found in gneiss have once been stratified, and that they have suffered some posterior changes by which the appearances of this disposition have been obliterated.’ Prof. Bonney has given a valuable description of the dynamic phenomena so well illustrated in thin sections of the Tiree Marble. Prof. Cole & Prof. Sollas have suggested that the Tiree Marble may originally have been a wind-blown coral-sand rock, with abundant rounded crystals of detrital augite, etc., such as was found on the east side of Mer, one of the Murray Islands. This theory appears untenable; for it is impossible to imagine a volcanic origin for the majority of the accessory minerals, which, with