Rocks of Noyang. 21 



Snowy River districts, with their associated fragmental for- 

 mations, tuffs, and lavas ; and finally, to the south, the course 

 of the Tambo River separates the lower palaeozoic sediments 

 to the west from a great extent of intrusive igneous rocks to 

 the east. 



III.— The Igneous Rocks. 



The particulars which I shall detail in these pages as to 

 the igneous rocks of Noyang admit of my now saying that 

 they are members of a series which is precisely analogous 

 to that of which granitite is the crystalline-granular type. 

 In this the characteristic felspar is orthoclase, while in the 

 Noyang series it is a plagioclastic felspar, and very frequently 

 albite. The complete analogy between the two groups of 

 rocks will be better seen when I come to the description of 

 the varieties of igneous rocks at Noyang. 



(a.) The Quartz-Mica-Diorites. 



Almost the whole of the south side of the Tambo River is 

 occupied by light-coloured crystalline-granular quartz-mica- 

 diorites. They do not, however, extend up the course of 

 the Tambo River for more than a mile above the Noyang 

 crossing, where they adjoin a great mass of quartz-mica- 

 porphyrite, of quartz-porphyrite, and of quartz-granophyrite, 

 which there crosses the river and extends for several miles 

 to the west along the course of the Haunted Stream. On 

 the eastern side of the Tambo, at Noyang, these quartz- 

 mica-diorites extend towards Mount Elizabeth for some 

 distance, and there also adjoin porphyritic varieties of rocks 

 of the same series. These porphyritic rocks have cut across 

 the crystalline-granular quartz-mica-diorites, have sent out 

 great masses into them, and also many strong dykes across 

 them even far into the adjoining sediments. Higher up 

 the course of a stream having its source in part of the 

 Mount Elizabeth Range, and near the localities I have 

 just mentioned, there are again large masses of a crystal- 

 line-granular character, which differ, however, in so far that 

 they seem to be somewhat younger in period of formation 

 than the quartz-mica-diorites which I have described, and are 

 also comparatively wanting in the basic minerals (magnesia- 

 iron-mica and amphibole) which characterise them. Some of 



