The stratigraphy of late Precambrian metasediments between Glen Roy and Lismore

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Abstract
Synopsis: The Moinian and Dalradian stratigraphy of the Glen Roy-Lismore area is systematically described and its terminology and definition is revised. The highest formation of the succession, the Lismore Limestone Formation, is of Lower Dalradian age and stratigraphically underlies the Portaskaig Boulder Bed. Succession, Glen Roy-Lismore. Thickness Islay Middle Dalradian Portaskaig B. B. LOWER DALRADIAN Ballachullish Group Lismore Limestone Fmn. ~1200 m Islay Limestone Fmn. (lower part correlated with Lismore Limestone Fmn.) Cuil Bay Slate Fmn. 300 m Appin Phyllite Fmn. 250 m Appin Limestone Fmn. 150 m Appin Quartzite Fmn. 300 m Ballachulish Slate Fmn. 400 m Ballachulish Limestone Fmn. 250 m Lochaber Group Leven Schist Fmn. ~2000 m Glen Coe Quartzite Fmn. 400 m Binnein Schist Fmn. 400 m Binnein Quartzite Fmn. 300 m Eilde Schist Fmn. 400 m Eilde Quartzite Fmn. 600 m Moinian Eilde Flags Fmn. >1000 m At Loch Leven the Lochaber Group is 4 km thick and the entire Lower Dalradian succession 7 km thick. To the north and west the quartzite units wedge out and the succession thins to about 5 km. This regional disparity is attributed to major facies changes and not structural modification as previously maintained (Bailey, 1934). There is a sedimentary contact between the Moinian and Dalradian Assemblages across most of the area. A detailed geological map of Lismore Island is presented together with a stratigraphic table of the Lismore Limestone Formation, which comprises a thick, partly cyclical sequence of alternating limestones and slates. The Eilde Flags Formation, the Lochaber Group and the Ballachulish Group constitute three lithological associations, each diagnostic of particular depositional conditions within a shallow shelf sea environment. The chemical compositions of the limestones and slates are tabulated and briefly discussed.

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