132 Charles Fenner: Quartz in Basalt, 



Some reasons have already been advanced to show that this might 

 not answer in the case of the Mount Greenock occurrence. The chief 

 points were — (a) The difficulty of forming a mental picture of any 

 means whereby the quartz could be " picked up " by a viscous, 

 stream, which is really not " flowing " in the same sense as water 

 flows; (b) the extent of the chemical inter-action between the quartz, 

 and the containing rock. 



As stated by Diller, in his discussion of this matter, all quartz 

 grains in a basic lava, whether native or foreign at the time of its 

 effusion, " would be subjected to the same conditions, all would be 

 corroded by the magma, and each have its re-action rim of pyroxene 

 formed." Still, the amount of inter-action must be largely depen- 

 dent on the heat of the magma at the time the quartz was " picked 

 up." Clarke, in his Data of Geo. -chemistry, p. 282, gives the 

 temperature of emerging lavas as " rarely if ever below 1000 deg. C. r 

 while the actual temperature not long before emission may be 

 hundreds, perhaps 1000, degrees higher." The most reliable data 

 as to the fusion point of quartz give its transformation to tridymite 

 at 800 deg. C, and subsequent fusion at about 1625 deg. C. Geikie 

 records that " lava from Terre del Greco fused the sharp edges of 

 flints." 



In the occurrences under discussion, however, the amount of cor- 

 rosion has been very great, the embayed quartz in some cases show- 

 ing traces of having been originally twice as large. In the scoria, 

 as has been described, the only minerals showing corrosion are the 

 quartz, and the olivine, suggesting that both these minerals were 

 in the molten material before ejection. 



Efforts were made, in the assay laboratory at the Ballarat School 

 of Mines, to reproduce the supposed conditions of " picked up " 

 quartz. Some normal basalt was melted, quartz was dropped in, 

 and the process of cooling retarded as much as possible. Sections 

 were then cut and microscopically examined. Owing to lack of a 

 proper control over the cooling, the crystallisation was not sufficient 

 to enable any observations of value to be made. 



In conclusion, while the Victorian occurrences, as so far investi- 

 gated, have shown no striking characters, they appear to suggest an 

 intratelluric origin of the quartz, and are of sufficient interest to 

 have some bearing on the still unsettled question of the origin of 

 quartz in basalts. With our hundreds of square miles of basalt still 

 uninvestigated, some facts may yet be brought to light that will have 

 n closer bearing mi the problem. 



