1 26 DREDGINGS OF THE MARINE BIOLOGICAL ASSOCIATION : 



shade being clue to a secondary mineral. This traverses the crystals 

 along irregular cracks, and sometimes extends from them a short way 

 into the ground-mass, continuing the line of the crack ; it is also 

 generally distributed in the crystal. The less altered felspar is pale 

 red in colour. The green mineral is often fibrous and sometimes 

 granular, it has a high double refraction ; apparently we are dealing 

 with epidote. Quartz crystals, somewhat corroded, are rather common, 

 and show a fair number of very minute fluid inclusions with bubbles. 



Titanic iron ore is scattered in small grains throughout the slide, 

 but much more freely developed and in larger forms at some places 

 where associated with the green decomposition product above referred 

 to. All the ilmenite is much altered and the smaller crystals are now 

 entirely leucoxene. Apatite occurs, and two much altered areas were 

 once apparently mica. 



QUARTZ-DIOEITES, DIORITES, DOLERITES, AND DIABASE. 



It is possible that exception may be taken to the manner in which 

 some specimens have been placed in the subdivisions of this group. 

 But the erection and maintenance of hard and fast boundaries, where 

 none such exist in nature, invariably brings the element of personal 

 judgment into play, and in most cases it will be found that ample 

 detail is given to enable the reader to reclassify the specimens to his 

 individual preferences. 



No pretence can be made that any more than a few, and those the 

 most representative, of the rocks in this group are here given. 



QUARTZ-DIOEITE. 



M. 11, 1, S. 26° W. Edd., 17- 8 miles. 



Brownish granitoid rock of medium grain. Texture granitic. Fel- 

 spars clouded light brown, but wherever the structure is not masked 

 by this show very closely repeated twinning. Outside the better 

 defined crystals there is some clearer and probably secondary felspar. 

 Quartz plentiful, traversed by streams of fluid inclusions in two or 

 more directions. The cracks in quartz and felspars alike are iron- 

 stained. Hornblende in short, well-marked, prism forms, pleochroism 

 light brown to rich green, two twinned crystals. Ilmenite occurs both 

 in hornblende and in felspars. A few minute crystals of apatite. 

 Quartz hornblende diorite. 

 M. 72e. S. 23° W. Edd., 19 miles. 



Pale green rock, with close texture and fine grain, black or very dark 

 green spots of small size. 



Micro-granitic structure. The minerals are felspar, quartz, horn- 

 blende, magnetite, mica, and augite. The felspars are clear in patches, 



