10 MR. E. H. CUNNINGHAM-CRAIG OX [Feb. I904, 



2. Metazviorphism in the Loch-Lomond District. By E. Hubert 

 Cotjningham-Craig, Esq., B.A., F.G.S. 1 (Read November 4th, 

 1903.) 



[Plates II-V: Microscope-Section?.] 



Contents. 



Page 



I . Introduct ion 10 



II. Dynamic Metamorphism 11 



III. Constructive Metamorphism 12 



I V. Nature of the Folding, and Stratigrapbical Eelations 13 



V. Petrograpbical Descriptions 15 



(a) The Leny-Grit Group. 



The Abei-foil-Slate Group. 

 u) The Beiun-Ledi Group. 

 (d) The Green Beds. 



VI. Chemical Analyses 22 



VII. The Zones of Progressive Metamorphism 24 



VIII. Contact-Metamorphism 25 



IX. Nature of the Albite-Gneiss Metamorphism 26 



X. Recapitulation 27 



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 dis- 

 tinct 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 ' Expla- 

 nation 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 



1 Communicated by permission of the Director of H.M. Geological Survey. 



