[ 724 ] 

 XCII. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 636.] 



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

 Vice-President, in the Chair. 



'^pHE 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 meta- 

 morphism 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 beginning 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 quickly superseded by a constructive metamorphism, probably of 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 hydro- 

 thermal, constructive, metamorphism. 



2. 'On a Kew Cave on the Eastern Side of Gibraltar.' By 

 Henry Dyke Acland, Esq., E.G.S. 



This cave, discovered in 1902, is situated a short distance south 

 of the eastern end of the tunnel, which pierces the Rock from the 

 Dockyard on the western side to ' Monkeys' Quarry ' on the 

 eastern. It was opened by blasting operations ; and from 

 the opening thus made, 88 feet above sea-level, the floor falls to 

 the west. The main haU is about 70 feet high and 45 feet wide, 

 and has a smooth stalagmite - floor resting on breccia and a 

 stalactitic roof covering the limestone of the Rock. Its floor falls 

 to a point 19 feet above sea-level. The lower gallery descends at its 

 far end to little if anything short of sea-level. Its floor consists of 

 stalagmite resting on fine calcareous sand ; this on coarse sand, 

 followed by rubbly and calcareous grit, which in time rests on the 

 rock-floor of the cave at a depth of 15 feet. In the calcareous 

 grit are numerous well-rounded stones, some pierced by pholades. 



