334 PHocEEDiNas OF THE GEOLoaicAL SOCIETY. [Jiine 9, 



nected, though all traces of this have since disappeared by denuda- 

 tion. Yet the assumption that the first three veins especially are 

 intrusive appears to be singularly at variance with the mode of their 

 mineral connexion with the reef. The feature generally observable 

 between intrusive dykes and the surrounding rock (a division-line 

 between the quartz and granite) is completely absent. The granite 

 appears here, in fact, not at all unlike a zone of impregnation, 

 inasmuch as the quartz, some distance above the veins, shows first 

 scattered crystals and particles of felspar; these increase in quantity; 

 plates and small nests of black mica appear, and, whilst their num- 

 ber also augments, the mixture becomes more and more fine- 

 grained, and the passage to typical granite is insensibly completed, 

 the reverse process of change of this rock to reef-quartz commencing 

 again a few feet below. The definite thickness given to each gra- 

 nite-vein in the previous description has only reference to the zone 

 of typical granite ; if those portions of the reef above and below 

 which bear already a marked granitic character were to be included, 

 the width of each vein would perhaps be double that given. Even 

 the gold and the other minerals associated with it in the reef take 

 part in the above passage, for they have been found several inches 

 deep in the granite ; in the centres of the veins, however, none 

 could be detected. Mr. Salter, the Manager of the Alliance Com- 

 pany, presented to the Melbourne Public Museum several fine 

 specimens, showing the gradual change of quartz to granite, 

 examples of vein-granite with specks of gold, pyrites, &c., and also 

 one specimen from the lowest (fourth) vein, consisting of quartz, 

 granite, and metamorphie rock. Between the two latter, however, 

 the passage appears not to be so gradual, on account of the black 

 colour of the metamorphie rock, caused by its very micaceous cha- 

 racter along the line of contact, though in some places the two rocks 

 appear like difi'erent conditions (textures) of the same magma. 



As regards their intrusive character, there is also an inexplicable 

 discrepancy in the behaviour of the upper three and the lowest 

 granite- vein, viz. that if this last vein be considered to have 

 faulted the reef (a supposition all the circumstances certainly point 

 to), no reason can be assigned why the other veins should not have 

 done the same, seeing that they intersect the reef at angles equally fa- 

 vourable for the production of this phenomenon. A shifting of the 

 reef might perhaps have been caused by the second vein ; but as, from 

 the mode of intersection (figs. 5 & 5a), it would have taken place in 

 the direction of the strike, ^. e. the surface-portion of the reef moved 

 southward, no displacement might be apparent ; with the other two 

 veins, however, it ought to be as plain as with the fourth granite-vein. 



The minerals hitherto observed as associated with the gold in the 

 Nuggetty Eeef are the following: — 



Iron-pyrites. Occurring generally in patches, strings, and, though 

 rarely, in druses of small cubical crj^stals in hollows. 



Arsenical pyrites. Like the former ; seldom as perfect crystals 

 imbedded in solid quartz. 



