II.— Tertiary Ring Structures in Britain

Abstract

I. INTRODUCTION. The detailed investigation of the Tertiary plutonic districts of Western Scotland, begun by Dr. Harker in Skye, may now be regarded as completed by the researches of Dr. Cockburn1 in remote St. Kilda; and, except for St. Kilda, the main results obtained have been summarized recently by Dr. Thomas in the Geological Survey memoir dealing with Ardnamurchan. With many presentations of its various aspects already in print, it is with some hesitation that I choose for this address a subject connected with Tertiary igneous activity. Yet there remains in the Scottish districts and also farther south, in North-east Ireland, a field for much further research. It is partly on this account that I venture to give to you in brief outline a description of the ring structures met with in each district. For it is in the more definite recognition of these characteristic features that the chief advance in our understanding of the complexes has lain. In part also, my subject is chosen in continuation of the series of accounts of Scottish formations which the Society has published in recent years. In the first place, I shall briefly describe the structural features of each complex in turn, beginning with the relatively simple district of Ardnamurchan. Before doing so, it is necessary to refer to some general aspects of Tertiary igneous activity, and also to indicate the various characteristic forms taken by the intrusive rocks, and the rock-types chiefly met with. The concentration of intrusive activity in certain districts This 250-word extract was created in the absence of an abstract