and Igneous Rocks of Unsay. 79 



istic groups. In this ground-mass are porphyrinic crystals 

 of serpentinised olivine and larger ones of colourless augite. 



The crystalline-granular rocks, in a much jointed con- 

 dition, extend to 9. Some of them are fine-grained; 

 some coarser, and of a red or salmon colour. They are 

 traversed by veins of pegmatite or coarse aplite, and also by 

 compact veins of epidosite. I examined a sample of the 

 fine-grained variety, which I found to be a crystalline- 

 granular compound of felspar and quartz in nearly equal 

 amounts, together with some brown magnesia-mica. The 

 latter was first formed, and is extremely ragged, twisted, 

 and, in places, much chloritised. It has a little magnetite 

 associated with it. The felspars are of two kinds, some- 

 what large, very much eroded, even cavernous, crystals of 

 orthoclase, and less- was ted, or even almost well-formed, 

 crystals of plagioclase. The quartz fills in spaces. I have 

 no doubt that this rock is intrusive. 



From 9 to .10 similar rocks extend, where then com- 

 mence some contorted schists, having in one place fibrolite 

 and quartz as a lenticular foliation. These schists cease at 

 11, where they are cut across by a dyke dipping S. 10° W. 

 at about 70°. This dyke is micro-porphyritic. It has a 

 micro-crystalline ground-mass approaching to cryptocrystal- 

 line. This is composed of minute crystals of some mineral 

 which I cannot further determine than by saying that it 

 ma}^ be felspar. Besides these there are some crystals of 

 magnetite and minute grains of augite. In this mass there 

 are numerous small porphyritic colourless crystals of augite. 

 Frequently these crystals are broken, and their fragments 

 separated by the ground-mass. In other places several of 

 these crystals form groups. This rock seems to stand 

 among the diabases, very near to diabase-porphyrite. 



The schists extend to 12, but towards that spot their 

 foliation is less well-marked. They then give place to 

 crystalline-granular rocks like those I have described 

 between 5 and 6, and they contain patches of much-contorted 

 schist. The schists then recommence. In places there is 

 an alteration of schistose and crystalline-granular structure, 

 very suggestive of a process of recrystallisation. I have 

 attempted to give a representation of this appearance in 

 fig. 3 of Plate III., but I fear not successfully. The passage 

 from one structure to the other is more gradual than I have 

 been able to delineate. I prepared slices of part of this 

 rock. Under the microscope I found it to have obscure 



