FefroUxji/ (IikJ (icobniii of (Jiwensfon-ii. 135 



sagenitic- webs as in the similar rock from Diamond Creek. Idio- 

 morphie outlines of original felspar are abundant in the ground 

 mass of the rock. They are now replaced by carbonates and sericite, 

 and it is manifestly impossible to tell whether they are orthoclastic 

 or plaj.Moclastic. Abundant granular impellucid carbonate occurs 

 throughout the section replacing both plienocrysts and minerals of 

 the gi'ound mass. Tlie powdered rock effervesces readily when 

 dilute hydroihloric acid is added in the cold, proving that the car- 

 bonate is chiefly calcite. Iron pyrites is present in nearly all sec- 

 tions. It is often idiomorphic, consisting of the following forms : 

 — 110, 100, and combnations of 100 and 111. The crystals are 

 often surrounded by a rim of secondary quartz arranged radially 

 with respect to the crystal edges. Such quartz may possibly repre- 

 sent recrystallised silica, formed by the attack of sulphuretted 

 hyrogen <>r alkaline sulphide solutions on the original iron mag- 

 nesium silicates. 



Section No. 135. Brecciated porphyry. One Tree Hill. The 

 felspars in this section are not so greatly altered. Phenocrysts of 

 both <r,t]ioclase and plagioclase are present, but the former mineral 

 predominates. It is frecjuently very greatly sericitised and car- 

 bonated, and appeai-8 to contain microperthitic intergrowths of 

 albite. One plagif)clase phenocryst gave symmetrical extinctions 

 of 200 fvoin the albite twin lamellae, and had a refractive index 

 greater than quartz, indicating felspar near andesine. 



Section No. 125. Xenolithic fragments of sandstone are present 

 in places in this section. They show no resorption, and are com- 

 posed of angular and sub-angular quartz grains, flakes of muscovite, 

 and a little zircon, and brown tourmaline. 



Ihhiifd rockx from iJit- coti/ifrt/ east of Melbourne. — Acidic dyke 

 i-ocks (quartz poipliyry. felsite, and diorite dykes, of various 

 writers) aie faiily common in Victoria, associated with intrusions 

 of granite and gianodioiite. East of Melbourne they are fairly 

 numerous, and are known from Diamond Creek, Warrandyte, 

 Tomplestowe, Frankston. Kinglake, Ringwood. and several other 

 places. Similar locks neai- Steel's Creek, Lilydale and Mount 

 (Tiaham are prt)bal)ly the extrusive facies of the same magma. 

 These dykes are usually altered metasomatically. in much the same 

 mannei- as in the rock described above, from One Tree Hill, and 

 are <'ften traversed by, or associated with, auriferous quartz veins 

 wliieh almost invariably contain stibnite. Auriferous dykes a: u^ 

 known at Diamond Creek. Warrandyte, Templestowe, Kinglake, 



