222 PROCEEDINGS OF SECTION C. 



may be given of the processes of metamorphism of the Silurian 

 strata of Omeo, some account must be taken of the amount of 

 water included in them when they were laid down as mud and 

 sand in the Palteozoic oceans. This percentage of water could 

 not wholly or in great measure escape until the strata containing 

 it were raised above the sea level, and became freed from it partly 

 by outflow and partly by admixture with meteoric waters perco- 

 lating from the surface. 



I do not think that they were so elevated before being meta- 

 morphosed, and therefore there must have been in them a per- 

 centage of mineralized water, which became involved in whatever 

 mechanical and chemical changes affected the strata. 



The quartz of the plutonic rocks, and of the plutonic quartz 

 dykes such as occur at Omeo, shows that there was also a certain 

 amount of water in the magmas from which these rocks were 

 derived, although relatively small. 



Thus the conclusion is reached that this amount of water in 

 both classes of rocks may have acted as a solvent, and that the 

 solutions which reacted in the schists, which formed the aggrega- 

 tion of quartz and felspar round some of the eyes in the gneisses, 

 which regenerated the detrital material as mica, and which 

 deposited the quartz in foliations and elsewhere, are not solely to 

 be attributed to tlie action of enormous pressure producing fluidity. 

 But the new views regarding the production of plasticity in rocks 

 may lead to the disregarding of more simple explanations. 



The view which has recommended itself to me, is, that the mica- 

 schists and gneisses of Omeo were produced by the co-operation of 

 two causes — first, pressure which caused a scliistose structure and 

 an abundance of finely comminuted material, — and second, the 

 chemical action of mineral solutions which were partly contained 

 in the original rocks and partly produced during the long 

 continued course of increasing pressure and rising temperature. 



These views, which are suggested by the observations recorded 

 in this paper, are indeed almost those formulated by Lehmann 

 when 'speaking of the granite magmas in his great work.* That 

 this is so may lead to the reasonable belief that the explanation 

 is at any rate, in its broader features, a sound one. 



* Op. cit,, p, 54. 



