62 E. 0. Teale: 



3. Diorite. — This rock has not been observed in situ yet, but 

 fresh specimens are abundant in the river gravels, and, judging 

 from the most basic segregation patches in the granodiorite. it is 

 most probably that the diprite is magmatically related to the 

 granodiorite, and is no doubt associated with it in its occurrences, 

 The rock in hand specimens is medium grained, crystalline, of 

 dark colour, showng abundant hornblende and felspar. In thin 

 sections the structure is holccrystalline, inclining to panidiomor- 

 phic, but the ferromagnesian minerals are imperfect in this direc- 

 tion. The felspars are most abundant and appear to be almost 

 entirely triclinic. Quartz is rare, being present only as odd grains. 

 Fcri'omagnesian minerals are abundant, but bulk less than the 

 felspars. They consist of typical green hornblende and greenish 

 brown biotite. 



B. Lower Carboniferous. 



The age of these rocks is determined from the evidence of the 

 fish remains found in the Mansfield area, with which these beds can 

 be seen to be continuous. They form jDart of an extensive series 

 of sediments extending from Mansfield south-easterly into Gipps- 

 land. 



1. Basal Conglomerates. — These are not largely developed within 

 the area mapped, but small remnants are found directly overlying 

 the dacite porphyry on the slopes between Timbertop and the 

 Howqua, and one small outcrop, in the track near the top of Tim- 

 Ijertop Gap rests in the decomposed diabasic rocks. It contains 

 pebbles both of this rock and of the porphyry. Quartz and quartz- 

 itic rocks are perhaps the most abundant generally, but porphyry, 

 red jasper, and diabase can generally be recognised. 



2. RhijoUte. — This is a w^ell-defined sheet of variable thickness 

 w-liich at Timbertop amounts to about 600 feet. It generally rests 

 on the conglomerate, but occasionally this bed appears to be absent, 

 and it rests directly on the porphyry, as on the spur east of Black- 

 bird Creek. Upon it is found almost invariably either conglome- 

 rate or pebbly sandstone. 



The rock is distinct from the porphyry. It is more felsitic, with 

 fewer phenocrysts, which are entirely felspar and quartz. Flow 

 structure is generally apparent. The colour is generally red and 

 the rock is decidedly more siliceous than the porphyry. 



Thin sections show it to be typical rhyolite, but the specimens 

 examined are more ferruginous than those of Mount Wellington, 

 and the felspar phenocrysts, all orthoclase, are more abundant than 



