METAMORPIIIC ROCKS OF THE OMEO DISTRICT, GIPPSLAND. 215 



undulating foliations of secondary quai'tz. This character is one 

 which I have nowhere observed in the true mica-schists of Omeo, 

 which have resulted from the metamorphism of sediments. If 

 may be looked upon as one of the indications of the action of 

 pressure metamorphism upon once massive rocks. 



It is to be noted that the greater number of "eyes" which T 

 have examined from these gneisses, have proved to be orthoclase, 

 thus perhaps connecting these rocks with the porphyritic granites 

 rather than wdth the diorites of the neighbourhood. Yet the 

 structure of some of the larger of the " eyes" suggests that they 

 have been partly formed from the remains of originally por- 

 phyritic crystals of felspar, and partly by accretions of felspar 

 and quartz, arranged i*ound them somewhat in the " graphic" 

 manner, and being derived from the resolution of the abraded 

 materials. Such solutions as these, represent it would seem, the 

 " secretions" spoken of by Lehmann, in his explanations of 

 pressure metamorphism. The characteristic tails of broken-up 

 materials which are usually attached to the opposite ends of the eyes, 

 show clearly whence the innumerable fragments which form some 

 of the foliations have been derived. The structure of the " graphic" 

 parts, and the presence in them of ciystals of biotite, arranged 

 radially to the eye, the layers of biotite which extend from it, and 

 the envelope of biotite which usually encloses it, point clearly and 

 decisively to a compound origin, and to the co-operation of the 

 cause. One of these was mechanical and the other chemical. 



These crystalline schists then, resemble in no way those schists 

 which, as I have shown, are the metamorphosed representatives of 

 the Silurian sediments, although they are evidently rock masses 

 which have been subjected to re-arrangement of their parts by 

 pi'essure metamorphism. The numerous survivals of original 

 mineral constituents in a more or less fragmental condition, 

 point to the former origin of these beds as having been igneous, 

 the kataklastic structure in places of the neighbouring massive 

 plutonic rocks, their occasional tendency to a schistose habit, the 

 completely gneissic structure of some beds, and the completely 

 mica-schist structure of others, as at Mount Livingstone, are 

 stages of the same metamorphic process. It commences with a 

 mere crushing of certain portions of the igneous mass, and ends 

 with a complete re-arrangement of the materials of those rocks 

 which have been crushed and stretched out beyond their point of 

 resistance. 



That the condition of these rocks when subject to pressure 

 metamorphism, was not merely one of a partly crystallized 

 magma, is shown by the comminution of their constituent minerals, 

 especially of quartz, which was the last to crystallize. It is also 

 abundantly shown by the manner in which micaceous foliations 

 have been formed from the detrital materials along friction 

 planes. 



