I.—The Augen Gneiss and Moine Sediments of Ross-shire

Abstract

In the centre of Ross-shire, to the west and north-west of Ben Wyvis, there are large intrusive masses of granite gneiss lying in the midst of the sedimentary Moine schists. They have a N.N.E. strike and extend over a tract of country about 20 miles in length, from Loch Luichart, near Garve Station (Dingwall and Skye line), to Carn Bhren, within 3½ miles of Ardgay Station (Inverness and Wick line). A coarse augen gneiss with large elliptical eyes of pink orthoclase or perthite, sometimes 2 inches long, is the principal rock, but a finer-grained granite gneiss also occupies considerable areas, especially in the region of Carn Chuinneag (see Map, Fig. 1). Boulders of the augen gneiss have been widely distributed by ice, and are common on the shores of the Moray Firth, etc. For that reason the “Inchbae augen gneiss” has long been familiar to geologists, though little was known about the parent mass, except that gneisses of this type were exposed on the high road between Garve and Ullapool, particularly in the lower part of Strath Rannoch.