Discussion on the Grampian Group: a major Late Proterozoic clastic sequence in the Central Highlands of Scotland

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Abstract
P. J. Haselock & R. H. S. Evans write: An attempt to collate the many advances in the sedimentological and stratigraphical understanding of the Grampian Group is to be welcomed. However, the recent paper by Glover & Winchester (1989) ignores several major problems of interpretation of both the stratigraphy and structure of the Central Highlands and is a premature analysis of the region. Principal amongst these problems is their definition of the geographic and stratigraphic limits of the Grampian Group, and the implications which stem from this definition. Harris et al. (1978) assign the majority of the metasediments in the Central Highlands below the Appin Group to the Dalradian Supergroup. This is done on the basis of their structural and stratigraphic continuity with the rest of the Dalradian Supergroup and their entirely Caledonian ( sensu lato ) history. They termed these dominantly psammitic metasediments the Grampian Group. The Grampian Group is thus the lower part of a complex stratigraphic sequence continuing up into the Port Askaig Tillite, for which an age of c. 650 Ma has been suggested for sedimentation ( Downie et al. 1971 ; Pringle 1972 ). However, Piasecki (1980) and Piasecki & Van Breemen (1979 a , b, 1983 ) suggest that at least part of this succession has been deformed and metamorphosed during the Morarian Orogeny (750Ma) and used the term Grampian Division to describe broadly the same sequence of metasediments. The Ord Ban Subgroup (see Glover & Winchester, fig. 7) and its overlying rhythmites were assigned to the Grampian Division ( Piasecki 1980 ). It seems difficult