Discussion of the North Ballachulish Dalradian

Abstract

D r . A. H. H ickman writes: Dr J. L. Roberts (1976, this Journal 132 ,139–54) admits that he has not established the existence of the Ballachulish Syncline ( Bailey 1934 ). Roberts accepts Bailey’s stratigraphy, confirms the outcrop pattern and the D3 Stob Ban Synform but finds no evidence that the central outcrop of the Ballachulish Limestone Formation occupies the refolded inverted limb of a major recumbent fold. Bailey (1910) first postulated the Ballachulish Syncline to explain a vertical repetition of limestone, slate and schist which did not correspond to his concept of the area’s stratigraphic succession. However, it is now known that the Ballachulish Limestone Formation contains thick intercalations of black slate and, less commonly, phyllite ( Hickman 1975 , p. 126) so that no structural repetition need be envisaged at Callert. Bailey’s sections through the Ballachulish Syncline (e.g. Bailey & Maufe 1960, fig. 7) show that over large areas its core consists of a remarkably uniform thickness (about 100 m) of Ballachulish Limestone Formation underlain and overlain by Leven Schist Formation. From Glencoe to Coire Mhorair (2185 7585), Coire an Easain (2250 7495) and the ‘Windows of Etive’ the length: thickness ratio of this core is about 100:1. Bailey (Bailey & Maufe 1960, p. 83) suggests that the core may even extend farther SE to Beinn Doirean (but see Thomas & Treagus 1968) and NE to Kinlochlaggan. The writer considers that these various isolated outcrops of limestone are probably local intercalations within the Lochaber Group. Dr Roberts does not mention that to the