714 W. N. Benson — Origin of Serpentine. 



seated origin of the carbonating solutions. "Wilkinson 

 (1885) referred to " geyser-action' ' the formation of the 

 sinter-like siliceous rocks occurring at Hanging Rock in 

 the Nundle District, but the persistence of the occurrence 

 of the partially leached and more or less sinter-like 

 siliceous rocks here and there throughout the whole 

 length of the serpentine belt (over two hundred miles), 

 leads one to the belief that, while the production of the 

 ferruginous sinter from the siliceous carbonate rocks 

 may be merely the effect of surface-waters, the waters 

 that formed the main mass both of the serpentine and 

 of the carbonate rocks were either genetically directly con- 

 nected with the great intrusive mass of peridotite itself, 

 or were those which also formed the auriferous quartz 

 veins, occasionally containing pyrites and calcite, that 

 traverse the sedimentary and igneous rocks invaded by 

 peridotite. These veins seem to have been formed at 

 some rather indefinite time during the long period of 

 plutonic igneous activity which followed the intrusion of 

 the peridotites (middle Carboniferous) and ended with 

 the intrusion of granitic rocks before the commencement 

 of Mesozoic time, and it would be in accord with the views 

 of perhaps the majority of modern geologists to consider 

 that such vein-forming waters were derived in part at 

 least from plutonic sources, and thus indirectly from the 

 same magma which gave rise to the peridotite. The 

 highly undulose extinction of the quartz formed in these 

 siliceous carbonate rocks may indicate that they suffered 

 considerable strain, presumably in the orogenic epoch in 

 which these intrusions occurred ; though it may perhaps 

 have resulted merely from the strains that might be 

 set up in quartz, forming from opal by dehydration. 

 The point is, that if the carbonation was performed by 

 the magmatic waters, it follows almost necessarily the 

 preceding serpentinization was also. 



Similar carbonate talc rocks occur in New Zealand, and 

 are especially well developed near Hokitika, where they 

 contain numerous cubes of pyrites. Bell's description 

 (1906) indicates that they are closely similar to the 

 greis en-like pyritic carbonate rocks of the Nundle Dis- 

 trict, N. S. W., and Dr. Bell adds: "the presence of so 

 much pyrites indicates considerable solfataric action fol- 

 lowing or during the period of Poumanu (i. e. ultrabasic) 

 intrusion. ' ' 



