[ 71 ] 

 IX. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from vol. xxiv. p. 291.] 



Nov. 9, 1887.— Prof. J. W. Judd, F.R.S., President, in the Chair. 



rpTTF. following communications were read : — 



J- 1. " Note on the so-called ' Soapstone ' of Fiji." By Henry 



B. Brady, F.R.S. 



2. "On some Results of Pressure and of Intrusive Granite in 

 Stratified Palaeozoic Rocks near Morlaix, in Brittany." By Prof. 

 T. G. Bonney, D.Sc, LL.D., F.R.S., F.G.S. 



The Author briefly described the handed Palaeozoic slates in the 

 neighbourhood of Morlaix, and gave a general account of their micro- 

 scopic structure. They are greatly contorted and folded, and have 

 evidently undergone very severe pressure. The result of this, as it 

 appears to him, has been the development of minute scales of a 

 light-coloured mica, especially in the darker (originally argillaceous 

 bands) and certain corresponding changes in the more quartzose 

 layers. The cleavage-planes often cut the surfaces of bedding and of 

 this micro-foliation, which are parallel, at high angles, and so are of 

 the nature of "Atisiveichungsclivage." 



In certain places these banded slates, after they have attained the 

 aforesaid condition, have been affected by intrusive granites. The 

 result has been the intensification of the changes which were already 

 incipient. The quartz granules have been doubled in size, the flakes 

 of mica have become four or five times as large, the black material 

 of the argillaceous bands has been gathered into larger granules, 

 and seemingly reduced in quantity (probably by partial oxidation of 

 the carbon), and in some cases andalusite crystals or grains of con- 

 siderable size have been developed. The rock has become compara- 

 tively hard, instead of friable, and the cleavage-planes are " soldered 

 up " by the development of mica along them. In its general aspect 

 one of these banded rocks (where free from andalusite) bears con- 

 siderable resemblance, macroscopic and even microscopic, to one of 

 the less coarsely crystalline, distinctly banded mica-schists, supposed 

 by many to occupy a rather high position in the Archaean series. 



3. " On the Position of the Obermittweida Conglomerate." By 

 Prof. T. M C K. Hughes, M.A., F.G.S. 



The Author gave an account of a visit to the section at Ober- 

 mittweida, 50 miles S.W. of Dresden, where there is an apparent 

 intercalation of conglomerate and sandstone in a gneissic series. 

 West of the stream at Obermittweida there is seen a crushed but not 

 much altered conglomerate of felsite and other pebbles, above which 

 gneiss and mica-schist rest, apparently in true sequence nume- 

 rically. Below the conglomerate no rocks were seen, but at a little 

 distance to the eastward coarse flaked muscovite-schists and gneissic 

 rocks were exposed, apparently underlying it. By a diagram the 

 Author showed how the conglomerate might belong to much newer 

 beds caught in a synclinal fold of the schists, and he advanced various 

 arguments in support of this explanation. 



