J. E. Treaguswrites: I am puzzled by the title of the paper b Evans & Tanner (1996), in which they propose to correlate the Kinlochlaggan Boulder Bed with the Port Askaig Tillite Formation. According to Harland (1990), the Vendian is the period preceding the Cambrian and divided into two epochs, the earlier Varanger and the later Ediacara. It is with this early Vendian Varanger epoch, that the Port Askaig Tillite Formation of the Dalradian of Scotland and Ireland can b broadly correlated. As far as I am aware, the late Vendiain Ediacara epoch contains no glaciogenic materials.
The real subject matter of the paper, however, is the authors’ proposal of the stratigraphical and structural position for the Kinlochlaggan Boulder Bed (KBB). Contrary to my original suggestion (Treagus 1969) that the KBB lay in an upward-facing succession which could be correlated with the lower par of the Appin Group, they propose that it lies within an inverted succession which can be correlated with the upper part of the Appin and lower part of the Argyll Group. I considered the latter correlation (Treagus 1969), but rejected it on the grounds of dissimilarities of the lithologies involved, am the greater similarities with the succession near the base of the Appin Group.
Without repeating the broad similarities of the two successions in the alternative correlations, I would like to make the following points, in favour of my original interpretation.
(1) The succession of pelites and psammites above the KBB frequently contain microcline perthite