METAMORPHIC ROCKS OF THE OMEO DISTRICT, GIPPSLAND. 213 



tourniiiline. These appeai'ances, thei'efore, prove tliat the faulting 

 of the strata was accompanied by intrusion of tlie igneous rocks, 

 and this seems to have taken place not only laterally, but also 

 from below upwards, suggesting that the schists were letdown 

 into the granitic magma. 



The metamorphism of the sediments was twofold and successive. 

 First, tliey were converted into argillites, and more rarely into 

 phyllites over a vast extent of country, and as it seems to me 

 through the action of the earth stresses which folded and crushed 

 the strata together. This process was in one sense mechanical, 

 and may be spoken of as Regional-Metamorphism. Second, tlie 

 altered sediments were subjected to a further metamorphism by 

 being invaded by the granitic magmas. The changes hei'eby 

 produced were, it would seem, not mechanical, for the strike 

 and dips of the beds appear not to have been altered. The 

 changes produced were in the production of a greater amount of 

 muscovite and biotite, and in the larger size of the individual 

 mica plates, in the increase of quartz in some beds, and finally in 

 the abundance of tourmaline generated throughout the whole of 

 the schists for some distance from the plutonic rocks. These latter 

 changes were, therefore, chemical, and appear to have been not 

 only the molecular rearrangement of the constituents of the 

 sedimentary beds, but also the introduction of silica, boron and 

 probably fluorine. 



It will be well now to say, once for all, that in the part of the 

 Omeo district with which I am now concerned, there are not any 

 true contact schists of the hornfels type. These are, however, 

 largely developed round the margins of some of the intrusive 

 areas which border the crystalline schists, for instance at Swift's 

 Creek, and at Noyang.* 



In proceeding from the great fault which I have now briefly 

 mentioned, in the direction of Mount Livingstone, that is to say, 

 into the tracts of the more crystalline schists, the rocks which 

 are first crossed are massive porphyritic granites, then schistose 

 rocks of a gneissic character, then near Mount Livingstone a 

 series of bedded gneisses, some of which have that structure 

 designated " augen gneiss." Finally there is reached beyond 

 them a tract of massive holocrystalline rocks which, as far as I 

 have examined them, are varieties of quartz diorites. These 

 extend westward in connected areas, flanked more or less by 

 gneisses to the eastern side of the Dargo Valley, where, as I have 

 already said, there is a further series of schistose rocks which 

 form the western margin in the metamorphic area. 



Similar observations may be made in proceeding from Mount 

 Livingstone to the Great Dividing Range, near Mount Birregun, 

 in the south-west, and towards the sources of the Kiewa River, 

 in the north-west. 



*The Diorites and Granites of Swift's Creek. Trans. R. See. Victoria, xvi. p, 61. The 

 Rocks of Noyang, op. cit. xx. p. 18. 



