234 



mass of small felspar lathes and aciciilar crystals of hornblende. 

 There is also a little brown biotifce. 



The felspar of the phenocrysts has extinction angles of about 

 16 from the albite twinning, and is probably oligoclase-andesine. 

 Most of the felspar of the ground mass is probably oligoclase. 



This rock with others w^as given to me by Mr. James Murray, 

 who was with Sir E. Shackelton's Expedition to the South Polar 

 regions. The rock was not found in situ, but was glacier-borne 

 by land ice from the south. 



{January \Qth, 1911.) 



Charles H. Caffyn : Hornhlende Schist, Aberystwyth, Wales. 

 This is a good example of a schistose rock caused by pressure 

 (Dynamic metamorphism). 



It was no doubt originally a plutonic diorite composed of 

 felspar and hornblende with a little iron ore, but the constituents 

 have now been crushed and spread out with a marked parallel 

 arrangement. The streaking out of the iron ore (probably 

 ilmenite) is well displayed, the felspar is broken up and re- 

 crystallised as a mosaic, and the hornblende, which was originally 

 in fairly large-sized crystals, has been fractured and the smaller 

 pieces are elongated in the direction of the vertical axis. Some 

 of the crystals show the process of breaking down. 



The ilmenite (titaniferous iron ore) is altering into granules 

 of leucoxene, a variety of sphene. 



The rock was not found in situ, but was picked up on the 

 beach. It probably came from one of the schistose complexes 

 of Carnarvonshire or Merioneth. 



{February iUJi, 1911.) 



Charles H. Caffyn : Orbicular Diorite, Corsica. The diorites 

 are plutonic rocks essentially composed of plagioclase felspar and 

 hornblende. 



Orbicular texture is one produced by more or less spheroidal 



