METAMORPIIIC ROCKS OP THE OMEO DISTRICT, GIPPSLAXD. 211 



THE CRYSTALLINE SCUISTS OF OMEO. 



When I came to examine critically the main tract of crystalline 

 schist by tlie light of the observations made along its boundaries, 

 I saw that there were also within these large areas of 

 holoerystalline rocks which might pi'ove to be intrusive, and not 

 as had been assumed, the ultimate result of the metamorphism of 

 sediments in situ. Thus I came to see further that the schists 

 themselves, which appeared to range from fine-grained nodular 

 mica-schist to coarse granite-gneiss, required to receive a further 

 examination in order to determine whether there were, in fact, 

 at Omeo, as had been supposed, an actual passage from the normal 

 Silui'ian sediments thi-ough mica schist and gneiss to massive 

 rocks, having a granitic character. 



Fortunately for such an investigation, a series of violent and 

 unprecedented floods had, some years before the time I speak of, 

 swept out the course of sevei-al streams to the bed rock, in 

 positions favourable for examining the supposed sequence. Thus 

 it was that I found myself in a position to take up an enquiry 

 which has led me to the views and conclusions embodied in this 

 paper. 



The great series of argillaceous and arenaceous beds which, for 

 reasons which I have already given, I regard as Silurian, is found 

 more or less connectedly to surround the area of the crystalline 

 schists. The strata have been tilted at high angles in a strike 

 usually approaching north-west and south-east. Microscopical 

 examination of a number of thin slices of these rocks leads me to 

 say that their general composition may be described as one in 

 which the original argillaceous paste has been more or less com- 

 pletely converted into minerals of the chlorite group, while in 

 some cases the original elastic grains of quartz have been enlarged 

 by the addition of secondary silica. The condition of these 

 Silurian formations is, therefore, that of one of the earlier stages 

 of metamorphism, impressed upon them during the process of 

 folding together of the strata, the tilling of the beds, and the 

 crushing of their materials. The most appropriate term for such 

 beds as these seems to be argillite, and in places the effects of 

 slaty cleavage are well marked. In certain parts of the Omeo 

 district, and notably where the argillites border the crystalline 

 schists, the former have been subjected to still further changes. 

 The general appearance of the beds remains the same as before, 

 the characteristic alternations of argillaceous and arenaceous beds 

 still continues, but on the cleavage planes there appears a silky 

 sheen, and the planes themselves are frequently minutely corru- 

 gated. The internal structure has, however, undergone a complete 

 change. The chlorite minerals have almost or wholly disappeared. 

 The carbonaceous or graphitic admixture is diminished or absent, 

 and the structure of the rock is now that of a mica-schist of 



