GEOLOGY OF ERUPTIVE AND ASSOCIATED ROCKS, POKOLBIN. 385 



Gap rocks has been determined on similar evidence, and 

 by the fact that a tuff bed has been found containing 

 Carboniferous fossils. 



A very definite and persistent horizon of Lower Marine 

 conglomerate can be traced in many places from " Maluna" 

 homestead as far as Mount View; this forms a very con- 

 venient datum bed, as it immediately overlies the Carboni- 

 ferous rocks. The conglomerate is unfossiliferous and, 

 apart from local inclusions of the underlying rocks, is 

 characterised by very mucli rounded pebbles of quartz-por- 

 phyry and quartzites from some unknown locality. The 

 conglomerate can be traced on both the eastern and western 

 sides of the Mount Bright area. At one point on the 

 western side, about one and a-half miles north of Mount 

 View School, a beautiful section shows the sequence from 

 the Carboniferous rhyoiite through Carboniferous con- 

 glomerate, shales and grits to Permo-Oarboniferous con- 

 glomerate and sandstone. At this point the latter are at 

 least 200 feet thick, the unconformity between them and 

 the Carboniferous being very slight. 



That the Mount Bright grano-diorite is considerably 

 older than the Carboniferous rhyolites has been definitely 

 proved by the finding of pebbles of grano-diorite in the 

 rhyoiite and tuffs at different points along the junction 01 

 the two rocks. Since considerable denudation must have 

 been necessary to lay bare the plutonic rock before the 

 rhyoiite flowed over it, the grano-diorite must be referred 

 to the Lower Carboniferous or some anterior period. 



Geology of the Three Areas. 



A — Carboniferous Rocks. 



The Drake's Hill Area. — The rocks consist mainly of 



rhyoiite, rhyoiite breccias and tuff, trachyte, and a number 



of isolated patches of andesite. The rhyolitic rocks are 



Y— Dec. 6, 1911. 



