Metamorphism in the Loch-Lomond District

I. Introduction. This communication has been written, not so much with the idea of describing any phase of metamorphism specially interesting in itself, as of contributing to our knowledge of what metamorphism is, and of distinguishing between different kinds of metamorphism. The term ‘metamorphism,’ or even ‘progressive metamorphism,’ has so often been used in a somewhat vague sense, without any distinct specification as to whether dynamic, thermal, hydrothermal, or contact-metamorphism, or a combination of two or more of these, is meant, that a study of an area where each of these types can be readily distinguished by its effects and considered separately, may prove of interest, as indicating the nature of those problems which workers among the Highland rocks have to investigate. In the ‘Loch-Lomond District’ I include all the Highland rocks on both sides of the loch, as well as the area lying to the eastward, including the Trossachs-—in fact that part of the Highlands which is embraced by Sheet 38 of the Ordnance-Survey map. The material for this paper was collected two years ago, after four years of work in the district, and the main conclusions will appear in the ‘Explanation of Sheet 38’ by the Geological Survey of Scotland. It is well-known that, in passing north-westward from the Highland Boundary-Fault, the metamorphism is seen to increase in degree. The progressive metamorphism in the Loch-Lomond district can be considered under two heads—dynamic, and what, for want of a better word, I call ‘constructive’ metamorphism. These processes have in