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 diorite 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 holocrystalline, inclining to panidiomor- 

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

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

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

 Ferromagnesian minerals are abundant, but bulk less than the 

 . felspars. They consist of typical green hornblende and greenish 

 brown biotite. 



B. Lower Carhoniferous. 



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

 fish remains found in the Mansfield area, with w^hich these beds can 

 be seen to be continuous. They form part 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- 

 bertop 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. EhyoUte. — This is a w^ell-defined sheet of variable thickness 

 which at Timbertop amounts to about COO 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 porpliyry. 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 





