330 Transactions. 



are frequently packed together in nests of irregular grains. No glass is 

 visible in the slide. In another specimen the feldspar laths and augite 

 crystals are of larger size, and the structure, is occasionally ophitic. The 

 vesicular rock is noted by Mr. Laing as coming from a dyke, but I think 

 it has in all probability come from a flow, judging from its texture and 

 from its close resemblance to the dolerite from flows in other parts of the 

 island. On inquiry from Mr. Laing, I find that he is not certain on the 

 point, as the exposure was a small one, and not clearly visible. 



Ball Bay, East Coast of the Island. 



Two specimens come from this locality. They are grey in colour, 

 closer grained than usual, showing to the eye phenocrysts of oli\'ine and 

 augite. Under the microscope they appear to be the ordinary coarse- 

 grained basaltic type found elsewhere on the island. They have a specific 

 gravity of 2-82. 



Mount Pitt and Middle of the Island. 



A number of specimens come from the neighbourhood of Mount Pitt, 

 the highest point in the island, situated towards its north-west corner. 

 Two samples are from near the summit ; one of these is a fairly compact 

 rock and the other very scoriaceous, the former having a specific gravity 

 of 2-65. They are both pinkish-grey in colour. In section the compact 

 rock appears to belong to the doleritic type, with large olivine pheno- 

 crysts, fresh or with a brown fringe. The scoriaceous rock contains the 

 same minerals, and, in addition, there are broken-comb forms of ilmenite 

 and an occasional phenocryst of feldspar (med. labradorite). 



A specimen from what is known as the Pop Rock, a prominent physical 

 feature situated about half-way up the southern slope of the mountain, is 

 a dark grey, vesicular, and with specific gravity 2'71. Under the micro- 

 scope it exhibits large phenocrysts of olivine, some fresh, others stained 

 with iron oxide. Augite occurs in small grains in the groundmass, never 

 in large crystals nor with idiomorphic outlines, but usually packed in be- 

 tween the feldspar laths ; these appear to be a medium labradorite. Some 

 brown glass full of inclusions is also present. 



A specimen from Ghost's Valley, on the western side of Mount Pitt, 

 closely resembles this in general features, but it is very scoriaceous, with 

 the vesicles filled with alteration -products. 



Specimens similar to the usual type come from boulders scattered on 

 the Surface of the middle of the island. 



Philip Island. 



The rocks collected by Mr. Laing at this interesting remnant of a larger 

 land-mass prove in every case to be tuffs. One of these is largely com- 

 posed of lapilli of the size of a small pea, which under the microscope prove 

 to be formed largely of yellowish glass full of vesicles, and containing 

 crystals of clear olivine and augite and laths of plagioclase (med. labra- 

 dorite) with an occasional feldspar phenocryst. The vesicles are full of 

 decomposition-products ; in some cases this is calcite, and in others it 

 appears to be stained with chlorite. 



The most interesting feature of these tulfa is an inclusion of piukiah- 

 brown colour and fine-grained texture. In section it is composed of com- 

 minuted fragments of quartz, plagioclase, some orthoclase, biotite. and 



