VI.— The Marginal Intrusions of Ben Nevis; the Coille Lianachain Complex; and the Ben Nevis Dyke Swarm

Abstract

I. INTRODUCTION. Subject of Paper. —The igneous complex of Ben Nevis is one of many intruded into the metamorphic rocks of the Highlands in Lower Old Red Sandstone times. It consists of a central core of volcanic rocks resting upon schist which has subsided into, and is now completely surrounded by, the Inner Granite. This in its turn is two-thirds encircled by a slightly more basic, and earlier, intrusion known as the Outer Granite (Fig. 1). The two main schist formations into which the Ben Nevis complex is exteriorly intruded are the Leven Schists and the Ballachulish Limestone. On the north-west side, however, the igneous rock also comes in contact with the Eilde Flags and on the north side with black schist grouped with the Ballachulish Slates. The Outer Granite is in the main a strikingly porphyritic pink rock, but around seven-eights of its periphery there is a non-porphyritic margin of varying breadth (Fig. 2). Very similar rock types to those found in this non-porphyritic margin also occur in the small plutonic mass (with an outcrop of a little under one square mile) lying half a mile to the east of the extreme north-east corner of the Ben Nevis complex and about three miles south of Spean Bridge (Fig. 7). No detailed account of this intrusion has yet been published, and from the wood which covers part of its outcrop it is proposed to refer to it as the Coille Lianachain mass. It is with the latter, and with the non-porphyritic This 250-word extract was created in the absence of an abstract The author wishes to acknowledge the invaluable help rendered by Professor E. B. Bailey, Mr. A. G. MacGregor and Dr. G. W. Tyrrell in the preparation of the paper. Acknowledgement is also due to the Controller of H.M. Stationery Office for permission to reproduce Fig. 1 from the Geological Survey Memoir on Ben Nevis and Glen Coe (1916) and for the loan of the block, and to the Institute of Quarrying for permission to reproduce two illustrations from the “Quarry Managers’ Journal” (March, 1934). He wishes also to express his thanks to the Geological Survey for offering every facility to examine maps, sections and other material. The cost of analyses and part of the cost of publication has been defrayed by a generous grant from the Carnegie Trustees for the Universities of Scotland.