Reports and Proceedings — Geological Society of London. 573 



in the treatment of the rocks ; but there are at the end of this 

 section a few pages dealing with petrogenesis and chemical classi- 

 fication, too condensed to be of much service. 



The second section, on the sedimentary rocks, is concerned with 

 precipitates (rock-salt, etc.), tufis, sandstones, sinters, limestones, 

 clays, etc. ; while the third is devoted to the crystalline stjhists,. 

 a term used in a rather wide sense to include gneisses, granulites, 

 mica-schists, eclogites, etc. 



The work, though not professing to offer original information, 

 will be found a useful handbook of descriptive petrography. It is 

 clearly written ; and the illustrations of the micro-structures of 

 rocks, simply designed, are well adiapted to their object. The only 

 statement which we have to quarrel with occurs on the title-page, 

 where the publication is post-dated by some two months, 



A. H. 



s,e:poe,ts .A.35rnD I=•I^OGEJ5]x:)II<^a-s. 



Geological Society of London. 



November 4th, 1903.— Sir Archibald Geikie, D.Sc, F.R.S., 

 Vice-President, in the Chair. 



The Secretai-y announced the presentation, by Sir John Evans,. 

 K.C.B., D.C.L., F.R.S., For. Sec. G.S., of a platinotype portrait of 

 himself. 



The following communications were read : — ■ 



1. "Metamorphism in the Loch Lomond District." By E. Hubert 

 Cunningham-Craig, Esq., M.A., F.G.S.^ 



The area dealt with includes all the Highland rocks on either 

 side of the Loch, as well as the area lying to the eastward, including 

 the Trossachs. Each stage of the progressive metamorphism can be 

 accurately determined, and each process can be studied, as a rule, 

 without confusing its effects with those of another process. The 

 rocks from the Leny Grit Group and the Aberfoil Slate Group show 

 dynamic metamorphism, which increases on a higher stratigraphical 

 horizon — the Beinn-Ledi Group ; and at Rudha Mor the beginnings 

 of the thermal type is seen. This is quickly superseded by 

 a constructive metamorphism, probably of hydrothermal type, 

 under which, combined with, or preceded by, the increasing- 

 dynamic metamorphism, the rocks become more highly crystalline, 

 until all clastic structures are obliterated. The segregation of like 

 minerals into folia, the total recrystallization, and the genesis of new 

 mineral groupings, result finally in the production of coarsely 

 crystalline albite-gneisses from a series of fine and coarse siliceous 

 and felspathic grits. Contact with plutonic igneous masses 

 obliterates many of the results produced by hydrothermal, 

 constructive, metamorphism. 



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



