/(/neons Pehhle.s. 298 



place at the expense of the original glassy ground mass. He men- 

 tions that in certain specimens of rocks from New South Wales 

 received by him from Professor David, the outgrowths apparently 

 took place after advanced kaolinisation of the original crystals. 

 In the Walhalla specimens, the latter remarks apply equally well, 

 with the substitution of sericitisation for kaolinisation. 



A moderate amount of interstitial quartz, containing fluid and 

 glass inclusions, is present in this section. It is doubtful whether 

 the quartz is primary or not. Considerable changes have taken 

 place in the rock, and it is possible that the quartz was formed 

 at the time of the amphibolitisation of the original femic mineral 

 which Avas probably augite. A little chlorite (pennine) occurs 

 replacing the hornblende, specimen W4, from same locality as 

 W2. This rock resemljles the preceding one very closely. Quartz 

 however is rare. Sub-ophitic hornblende, and plagioclase laths 

 predominate. The plagioclase appears to be present in two genera- 

 tions. An analysis of this rock for silica and alkalies gave the 

 following result : — 



SiO^ 52.99 per cent. 



Ko 2.09 per cent. 



Nao ... 3.21 per cent. 

 The analysis confirms the microscopical determination of the rock 

 as a hornblende diabase, or according to Barker's nomenclature, 

 a hornblende dolerite. Since the hornblende is secondary, pre- 

 sumably replacing augite, the rock may be described as an epi- 

 diorite. No unequivocal potash felspar is present in the section, 

 so that the relatively high percentage of potash indicated in the 

 analysis, is probably due to the extensive sericitisation undergone 

 by the original felspars. 



Basic spherulite {1 variolite). 



In hand specimen, this rock is compact and aplianitic, and green 

 in colour. No vesicles are seen even with the aid of a lens, and 

 in only one specimen collected was there any evidence of varioles. 



Section W6, pebble in conglomerate; section on road to the 

 Jubilee Mine. Examined microscopically, it is seen that the rock 

 is composed almost entirely of beautifully developed, sheaf and 

 fan like, and occasionally spherulitic aggregates of hornblende 

 and felspar. Phenocrysts are practically absent, as are also true 

 varioles marked off from the ground mass. According to the de- 

 finition of Professors Cole and Gregory, ^ " a variolite is a devitri- 



11 



