Metamorphic Limestones of the Great Glen Area: Reply

Abstract

SIRS—Rock et al. (1984)-highlighted the problems of assigning the limestones of the Great Glen to the Lewisian, Moinian or Dalradian but preferred to leave them unaffiliated. Following Drever (1936, 1939, 1940) we consider these limestones to belong to the Dalradian and propose that at least the Ardgour and Glen Dessarry limestones are the diachronous “missing links” between the Vendian Middle Dalradian basinal succession to the SE and the early Cambrian shelf succession to the NW (Fig. 1). We agree that the limestones do not correlate with the Lower Dalradian both on the geochemical grounds advanced by Rock et al. (1984) and also because of the general absence of authigenic K-feldspars in the Lower Dalradian, a mineral found in both the Ardgour and the Glen Dessarry limestones (Rock et al. 1984) as well as in the anhydrite-bearing dolomitic Fucoid Beds of early Cambrian age (Bowie et al. 1966; Allison and Russell 1985). Barrow (in Flett 1907) had mapped a calc-silicate horizon in the Middle Dalradian Deeside limestone that contains alkali feldspar. These Deeside rocks are favoured by Drever (1940) as being most comparable to the Ardgour limestones. Again in the Middle Dalradian, barium-rich K-feldspar has been found in the Loch Tay Limestone (Scott, pers. com. 1984) and we have found K-feldspar in the Shira Limestone.