134 DREDGINGS OF THE MARINE BIOLOGICAL ASSOCIATION: 



M. 80. S. 16|° W. Edd., 48 9 miles. 



Granitic texture. Brown-grey, fine-grained, black mica. 



Felsitic tcdure. Light brown-grey, ])lack mica, apparently a variant 

 of above. 



All the above granitoid rocks are described from megascopic ex- 

 amination only, and the list is inserted chiefly in order to point out 

 the localities in which this class of material has been found. To 

 adequately deal with all the varieties a great number of sections would 

 have been required, but probably those which have been microscopically 

 examined give a fair general idea of the whole. 



SCHORL ROCK. 



Eocks consisting of tourmaline and quartz ; placed liere, although 

 undoubtedly in a sense metamorphic, on account of their usual associa- 

 tion with granite. 



356/4a. W. i S. Bolt Head, 4| miles. 



A rather small pebble. 



This rock consists of quartz and tourmaline. Much of the quartz is 

 secondary ; in part it forms a mosaic, in parts it extends from original 

 crystals with which its crystal axis corresponds. The primary quartz 

 contains fluid inclusions with bubbles, the bubble in many instances 

 occupying more space than the fluid ; these inclusions are very 

 numerous and rather large. The secondary quartz contains few and 

 very small fluid inclusions. Acicular schorl is scattered throughout 

 the slide, sometimes in almost fibrous radial bunches, at others in 

 slender, well-defined prisms, radially or otherwise arranged ; there is 

 also some more massive schorl. The colour is chiefly light blue to rich 

 blue, but blue-green occurs, and occasionally olive-brown. 



M. 31a. S. 25° W. Edd., 15 miles. 



A schorl rock of Dartmoor type. 



Ground-mass a quartz mosaic. The quartz contains many fluid 

 inclusions, some of which, in addition to a bubble, have also cubic 

 crystals in the fluid. These cubic crystals are, in fact, very common. 

 The slide is crowded with granular tourmaline, chiefly a very dark 

 brown colour, almost opaque, but a few grains are blue-green. 



M. 31g. 



Schorl rock. The general ground of a brown shade, an intimate 

 mixture of rather pale brown tourmaline and quartz. Frequent areas 

 of quartz partially invaded by acicular tourmaline. Some cracks are 

 also filled by quartz. The quartz areas all present a mosaic, in 

 which some grains contain many more fluid inclusions with bubbles 



