On the Occurrence of TracJcyte in Victoria. \)7 



the Macedon rock and I see no reason to doubt that it is the 

 sanidine varity of orthoclase. The ground mass contains some 

 glass in which are set somewhat short, stout felspars, thus 

 giving the rock the structure designated by Rosenbusch as 

 orthophyric. These minute felspars have well marked crystal 

 boundaries, give straight extinction and show but little tendence 

 to flow arrangement. There is a small quantity of opaque 

 matter disseminated through the base. Apatite is present in 

 rather slender prismatic crystals, but mica, augite and horn- 

 blende appear to be absent. The rock must be classed as a 

 trachyte. Possibly its occurrence as a narrow dyke may account 

 for the glass seen in the base. 



Further north and on the opposite side of the creek is an 

 outcrop of a rock having a somewhat schistose structure. On 

 examination it is found to consist largely of felspar crystals of 

 columnar habit. In three slides prepared from this rock no 

 glass could be traced, but it may still be there as the dissemi- 

 nation of tine black dust through the base makes the slide 

 somewhat opaque. The matrix of the rock is mainly lath-shaped 

 microliths of felspar arranged somewhat in parallel lines. The 

 felspar phenocrysts are sanidine, showing in almost every 

 case twinning on the Carlsbad law, and very frequently the 

 characteristic rude parting parallel to the face (100). Horn- 

 blende is present in grains and ill-formed crystals. Mica, 

 magnetite and apatite may also be traced. 



From the low hill lying due north of the Koroit Inn, 

 Coleraine, and just beyond the Koroit Creek, a specimen still 

 more compact in structure and showing smaller porphyritic 

 crystals of felspar was obtained. On slicing it the phenocrysts 

 turned out to be sanidine, while the base was mainly microliths 

 of the same material. Augite quite destitute of crystal 

 boundaries occurs in considerable quantity and magnetite is 

 also present. 



A little north of west of the last mentioned hill are several 

 small quarries of what I took to be sandstone. The rock is 

 light gray in colour and medium grained in texture. No 

 phenocrysts can be seen with the naked eye. On slicing the 

 rock I was surprised to find that it is made up almost entirely of 

 felspar crystals. These are monoclinic and on comparison with 



