450 PETROLOGICAL NOTES ON N. S. WALES ROCKS, 



specimen is of medium grain-size, and is composed of labradorite, 

 subophitic augite, abmidant magnetite and a little ciuartz. The 

 augite has a peculiar spongy habit, containing felspar in irregular 

 patches and numerous schiller-magnetites. Here and there, in irre- 

 gular bays cutting across the large crystals, are patches of fine- 

 grained lathy felspar, small augite, ilmenite, and magnetite-grains, 

 with a general basaltic appearance. In such areas, there is some- 

 times a regular arrangement of the magnetite, as if pseudomor- 

 phous after a former crystal. These structures, together with the 

 spongy nature of the augites, suggest a partial recrystallisation of 

 the rock under the heat of the surrounding basalt-magma. The 

 large amount of decomposition-products in this rock greatly hin- 

 ders its elucidation. 



The inclusions of the metamorphic series are of several kinds. 

 One is an alkali-felspar gneiss, consisting of microperthite, ortho- 

 clase, quartz, and a very little plagioclase. It has a blastogranitic 

 structure, and the quartz shows, very strongly, marked strain- 

 effects. Another type contains. w4th orthoclase, a considerable 

 amount of andesine. A third type has a very gneissic structure, and 

 consists of abundant quartz, andesine, a little orthoclase, diopside 

 and sphene ; its composition is, therefore, that of a type of gTano- 

 diorite. There are, in addition, numerous fragments of felspathic 

 quartz-rocks. Several of these are very coarse-grained and poor in 

 felspar, resembling crushed vein-rock. The others are altered 

 quartzites, and are more or less felspathic. Both are greatly 

 crushed, with occasionally long mylonitic streaks, which lie along 

 the direction of crystalloblastic schistosity or obliquely to it. The 

 crystalloblastic structure is very pronounced; the felspar of the 

 vein-rocks is in large plates ; that of the schists proper is dissemi- 

 nated in small grains throughout the rock. 



The contact-effects may be divided into absorption, melting and 

 recrystallisation, and these occur frequently in association. The 

 first is well seen on the actual contact of an inclusion with the 

 basalt. The difference betwen the boundaries of the quartz-grains 

 and the felspars is most striking. As is usually the case, there is 

 a strong reaction-rim developed round the corroded surface of the 



