26H ' N. B. Junner: 



rook, showing a tendency towards a porphyritic structure. Zoned 

 plagioclase, having a nucleus of oligoclase or oligoclase-andesine, 

 and an outer zone of albite, greatly predominates over orthoclase. 

 Several traverses of this section showed that the ratio of plagioclase 

 to orthoclase was approximately ."3 : 1. One plagioclase phenocryst 

 shoAved a highly sericitised idiomorphic core surrounded by finely 

 zoned pellucid felspar. Orthoclase is present in simply twinned 

 phenocrysts, including a small quantity of microperthitic albite. It 

 is apparently identical with the type present in the neighbouring 

 rhyolites. Titaniferous biotite occurs as deep brown idiomorphic 

 plates. Some of the biotite has been bleached, and r utile needles^ 

 have separated out in the form of sagenite webs. Pleochroic haloes 

 due to inclusion of zircon are very noticeable in the altered mica. 

 Inclusions of ihnenite are also common. A little muscovite is also- 

 present, but it is undoubtedly secondary. Zircon and apatite a]e 

 common accessories. Tlie garnet crystals, which appear to be 

 homogeneous in hand specimens are seen under the microscope to be- 

 greatly fractured and to include unaltered and chloritised biotite, 

 quartz, ilmenite and apatite. Rims of biotite often surround the- 

 garnet crystals. 



Maroondah (iqutdnci , north of Uealesvillt. — Granodiorite out- 

 crops on the ridge seijarating Meyer's creek and Donnelly's creek, 

 The rock is greatly decomposed near the surface, but fresh speci- 

 mens are obtainable froui the tips formed from the rocks taken out 

 in tlie tunnelling of the above-mentioned ridge for the Maroondah 

 aqueduct. At the western end of the tunnel contorted, steeply 

 dipping Silurian mudstones and .shales outcrop. Near the contact 

 the sediments have been changed to liornfels. Xenoliths of meta- 

 morphosed sediments are common in the granodiorite near the 

 coiitact. 



In hand specimen the rock is medium and even grained, and 

 consists of colourless quartz, felspar and abundant biotite. Pink 

 garnets are not uncommon. Fine-grained rocks (microgranite or 

 aplite) are occasionally present. 



Section No. HlOO, contact of granodiorite with sedimentary 

 Xenolith, from tunnel in Maroondah aqueduct. — The mineralogical 

 composition of tliis granodiorite is very similar to; that of the rock 

 from near Maloi-y's falls. The felspai-s. however, are greatly re- 

 placed by scrii-itc and carl)onatcs, and the brown biotite crystals 

 are greatly chloritised, and sagenitic webs of rutile have separated 

 o\it. A fail- amount of granular ilmenite occurs throughout the 

 section. Near the contact pyrrhotite makes its appearance in con- 

 siderable quantities, and the place of the granular ilmenite is taken 



