Notes on the Area of Intrusive Rod's at Bar go. 153 



minute markings, and that, moreover, this moulding was 

 completed after the crystals were formed. The fractures of 

 the schorl crystals^ the removal of the parts from each other, 

 the penetration of films of quartz into small fissures in the 

 crystals suggest that the silica, when this happened, was, as 

 a whole, capable of some movement under a degree of pres- 

 sure, and the moulding of the quartz to the schorl crystals 

 shows that it was plastic. The supposition that the quartz 

 may have been gradually deposited from solution round the 

 crystals of schorl until the fissure was completely filled seems 

 to be quite negatived by the observation that the schorl is 

 not attached to the walls of the fissure, but " fioats" free in 

 the quartz. This requires, therefore, that the quartz should 

 have been in such a state as would admit of movement, and 

 yet in a condition far denser than that of an ordinary solu- 

 tion. These observations on the mode of occurrence of 

 crystals of schorl in quartz veins are not new, but have been 

 made and recorded long ago.* I now mention the par- 

 ticulars, as I have seen them at Omeo, as being necessary to 

 the explanation which I desire to offer. 



It seems to me that the above facts admit of only two 

 alternative explanations. Either the quartz was in a molten 

 condition when it filled the fissure, or it was in the condition 

 of a solution in an extreme state of condensation. There is 

 no evidence whatever in the adjoining rocks of any such 

 elevation of temperature as would be necessary for the 

 fusion of quartz, nor do I think that at the present day 

 geologists would be inclined to admit an hypothesis based 

 thereupon.! There remains, then, the second hypothesis, 

 and this would be satisfied by the supposition that the 

 quartz had been forced into the fissure in a colloidal condi- 

 tion, accompanied by such plutonic emanations as would 

 suffice, together with small amounts of bases contained in 

 the colloid silica to the formation of schorl. 



* For instance, see Bischoff, "Lebrbuch der Cbemiscben, unci Pbysical- 

 ischen Geologie," Band II., 552. 



t I observe some remarks by Professor Kosenbusch, wbicb have a bearing 

 upon tbis question. He says (" Microskopiscbe Pbysiograpbie der Petro- 

 grapbiscb wicbtigen Mineralien" — 2nd Edition, p. 344): — "Eine darstellung 

 des quartzes aus scbmelzfiussigen silikat-mutterlaugen ist bis darbin stets 

 vergeblicb versucbt worden. Der Grund durfte darin zusucben sein, dass 

 die klinstlicben Silikat-scbmelzen nicbt wasserbaltig bergestellt werden 

 konnen, wie es die natiirlicben sind." 



