Mocks of the Hoicqua River. 03 



;the quartz. Secondary silicification is apparent in some sections. 

 ;No ferromagnesian minerals were noted. (Slides 26, 28, and .'>4.) 



3. Conglomerates. — This bed often passing into pebbly sand- 

 . stones generally overlies the rh^-olite almost everywhere in this 

 series. It is well developed at Blount Timtertop, where it passes 



!up into the normal sandstone. 



4. The sandstones are generally of a coarse texture, often flaggy 

 and micaceous, and with a reddi.sh colour. They form as a rule 

 thick beds which alternate with a purplish to chocolate coloured 

 shale, which sometimes has the appearance of an oxidised ash bed. 

 The shales generally provide good grazing country. The colour, 

 texture and generally low angle of dip of these rocks render them 

 readily distinguishable from' the older i"ocks in the field. Their 

 influence on the topography, too, is distinct. 



The alternation of hard and soft beds more or less horizontally 

 'disposed gives the hills in general a table topped and ledged ch.arac- 

 ter, so well shown in the neighbourhood of Mansfield. 



Summary and Conclusions. 



The area examined covers about 60 square miles of mountainous 

 • country, previously unmapped. It lies about 20 miles to the south- 

 east of Mansfield, and forms a portion of the central highland 

 region of Victoria. Physiographically it consists of an area of 

 high relief in an advanced stage of deep dissection. The original 

 plateau character is almoist completely obliterated. Deep valleys 

 <^•ith permanent streams separated by steep narroAv ridges occupy 

 the whole of the region. Small remnants of an overmantel of flat- 

 lying rhyolite and sediments are preserved, provirling a topo- 

 graphic contrast to the outline of the highly folded older rocks. 



The area lies in the drainage basin of the Upper Goulburn, and 

 the development of this river system as a whole is intimately con- 

 nected with interesting tectonic and structural questions. 



The main problem dealt with in the area concerns the occur- 

 rence of diabasic rocks and cherts closely similar to those of Heath- 

 cote, and their relations generally Avith reference to the Heath- 

 cotian problem in Victoria. 



The lithological resemblances are most striking, both with regard 

 to the diabase and its alteration products. The cherts occiipy a 

 similar relationship, and in each case contain Protoaiiongia. Con- 

 tact alteration features are absent, and the rocks for the most part 

 ■have the character of altered lavas and tuffsi of submarine origin. 



