292 PEOCEEDINGS 0¥ THE GEOLOGICAL SOCIETY, [April 24, 



upper portion of the same formation, and occasionally throughout 

 the other beds. 



At Gympie, one of the richest quartz-reefing districts in the colony, 

 the auriferous area is confined to veins traversing a crystalline diorite, 

 or within a certain limit of its boundary, marked by the presence of 

 fossiliferous diabase tufas. 



Of the crystalline rock at Gympie Mr. Aplin, who reported on the 

 district, gives the following description : — 



" In irregular-shaped masses or broad dykes this rock occurs at 

 intervals over a large portion of the area of this gold-field, but is 

 most prominently developed within a zone half a mile or more in 

 width, having a longitudinal direction of about N. 60° W., and 

 embracing the space from the ' Lady Mary ' hill to that on which the 

 Gympie township commences. 



" It is in the decomposed upper portions of this rock, which 

 weathers brown and argillaceous, though retaining its compactness, 

 that the quartz veins traversing it are found to be so highly pro- 

 ductive. 



" In its ordinary condition it is excessively hard, and is the most 

 formidable obstacle the miners have to contend with, some from 

 the very surface, and others at varying but comparatively shallow 

 depths." 



Of the lode-stones outside a certain limit from this crystalline rock 

 he says : — " The quartz-veins associated ivitli the slates or other sedi- 

 mentary roclcs not connected tvith, or affected hy, the greenstone have 

 hitherto been found not to contain gold in paying quantity T 



Mr. Hacket, who devoted a much longer time to the survey of the 

 Gympie gold-field, confirms Mr. Aplin's opinion on the latter point, 

 as he says in his report : — 



" Skirting the greenstone-belt on both sides is a series of siliceous 

 slates and quartzites, highly metamorphosed, and in many cases 

 jasperized, banded, and cleaved. 



" In this latter formation no gold has yet been found, although 

 many reefs have been explored." 



Mr. Hacket, however, seems to have thovight that the crystalline 

 rocks were interstratified with the slates &c. 



My own impression, formed from two short visits to this locality, 

 was that the crystalline rock was in all cases intrusive, whilst the 

 so-called " fossiliferous greenstone " was a tufaceous deposit, partly 

 contemporaneous with, partly the result of the denudation of the 

 crystalline rock which represented the core or cores of Devonian 

 trap-vents. 



The analysis of the two varieties of rock above mentioned, viz. 

 the so-called Gympie "greenstone" and the "fossiliferous green- 

 stone," gave the following results : — 



