122 DREDGINGS OF THE MARINE BIOLOGICAL ASSOCIATION: 



twinning of orthoclase shows in almost every one. Some of the 

 felspars are slightly tinted yellow liy powdery decomposition products. 

 The mica inclines to a reddish bronze lustre. The general structure of 

 the rock is very uniform. 



In the section a portion of the felspars is seen to be slightly clouded. 

 The more part are orthoclase, but the orthoclase at places encloses 

 small crystals of triclinic felspars, of which larger areas also occur. 

 There is a tendency to zonal structure in some of the felspars, and 

 there are a few very small areas of graphic structure. The quartz con- 

 tains fairly numerous fluid inclusions with bubbles, some apparently 

 empty or gas-filled cavities, and frequent hair-like microlites, probably 

 apatite. Almost all the mica is brown and intensely pleochroic, but 

 associated with this is a little which is colourless and shows no 

 pleochroism. Apatite is present. 



Boulder. S.W. by S. ^ S. Bolt Head, 19 miles. Weight 833 lbs. 



A coarse rock of granitic texture. The felspar gives bright cleavage 

 surfaces, but is largely yellow-stained by dusty decomposition pro- 

 ducts ; there are no good crystal outlines. Black mica occurs in 

 patches of granular texture. 



The large orthoclase areas are seen in section to be intergrown with 

 plagioclase, narrow irregular and only approximately parallel strips 

 of which penetrate the orthoclase ; all the strips in each crystal ex- 

 tinguish together and in a different position to the main crystal, and 

 all show lamellar twinning, the direction of which is constant through- 

 out the crystal ; thus the intergrowth gives rise to micro-perthite. 

 Those felspars, the less numerous, which are clouded with decomposi- 

 tion products, all appear to be triclinic. The quartz presents 

 numerous fluid inclusions, and in places is crowded with other in- 

 clusions which appear as a fine black dust ; there are also small 

 acicular microlites. The mica passes from olive-brown to dark green 

 on rotation, but there is a little that is almost colourless. 



M. 58b. S. 22° W. Edd., 39 miles. 



Medium textured granitic rock, pale flesh-coloured felspar, dark and 

 light mica. Structure granitic. Felspars clouded brown. There are 

 small patches of very well defined graphic structure, here the 

 felspar is clearer. Multiple twinning can still be detected in places. 

 Nearly half the felspar is still almost clear ; none of this shows plagio- 

 clase twins. Much colourless widely biaxial mica. Quartz plentiful, 

 crowded and lined by fluid inclusions, all with bubbles ; many of these 

 inclusions are of comparatively large size. There is a little apatite, 

 and in one part of the slide a chloritic mineral fills the cracks in a 

 felspar. 



