The Structure and Stratigraphical Succession of the Moines of Fannich Forest and Strath Bran, Ross-Shire

Abstract

Summary The order of deposition of metamorphosed Moinian sediments in an area a few miles east of the Moine thrust has been determined with the aid of current-bedding. The previously accepted succession is seen to be incomplete and inverted, and the structural interpretation based on it is therefore largely invalid. Within a succession some 13,000 feet thick, rocks formerly regarded as inliers of Lewisian appear at two horizons. The lower, forming the supposed inliers of Scardroy and Achnasheen, contains abundant banded hornblendic rocks; the upper, the so-called Fannich inlier, is dominantly siliceous. The major folds, with a wave-lenght of several miles, are overturned towards the west and are isoclinal only in the south. Their axes run, on the average, N.-S., but show much variation in the direction and angle of plunge. Relative variations in the plunge of an adjacent syncline cause the steep or inverted limb common to them both to change its thickness or even to disappear. Variations in plunge lead also to the formation of contemporaneous subsidiary flexures running NW.-SE. The relations of minor structures (small folds, cleavage and lineations) to the major fold system are discussed. I. Introduction The part of Wester Ross in the Northern Highlands of Scotland with which this paper deals (see Fig. 1) was mapped many years ago by the Geological Survey of Great Britain and described in two memoirs published in 1913 : one on the Fannich Mountains (explanation of sheet 92) and one on central Ross-shire (explanation of sheet 82). A small