Metamorpkic and Plutonic Bocks at Omeo. 125 



microperthites, except in so far that they are very minute 

 and in small amount. When the slice is placed in such a 

 position that the plane of vibration of the orthoclase is 

 parallel to that of the polarizer, the nicols being crossed, and 

 the field therefore obscure, the space surrounding any one of 

 the quartz inclusions depolarizes the ray, and permits light to 

 pass. Bat in the space thus illuminated a black cross shows, 

 whose arms are parallel to the ortho and clino-diagonals 

 respectively. On. rotating the slice some 3° from this position, 

 the arms of the cross close together into a black bar having 

 that direction, the field still being light. These appearances 

 indicate that the felspar surrounding the quartz grain is in 

 a state of strain. 



A slice prepared from the second cleavage, namely, parallel 

 to the clino-pmnacoid, shows the familiar appearance of 

 minute veinlets of the second felspar (albite), which cross 

 the trace of the perfect cleavage at an angle approximating 

 to 65°. The potassa felspar in this slice obscures at 5° 20' 

 referred to the same datum. 



These appearances explain the occurrence of soda in the 

 analysis, although the percentage found is larger than I 

 should have expected from the inspection of the two slices 

 which I prepared. 



The felspar is an orthoclase, intergrown with a proportion 

 of albite, after the manner of the microperthites. 



It will now be advantageous to summarise the results 

 to which these descriptions of the rocks lead me, first 

 commencing with the schists : — 



The schists which I have described occur only on the 

 north-eastern side of the contact, and extend thence for 

 some miles towards Hinnomunjie, the Omeo Plains, and the 

 Bowen Mountains. On the south-western side of the 

 contact there are no schists similar to these, but such as can 

 be found are of a more gneissose structure, with only 

 subordinate traces of mica schist. 



When the country is examined for a distance from the 

 contact on its eastern side, the inference seems to be justified 

 that the schists are the metamorphosed representatives of a 

 sequence of sedimentary formations, which can be seen in 

 their least altered forms in the Bowen Mountains ; more 

 especially on the eastern sides of these mountains, where, 

 between Tongeo and Bindi, they have the appearance of the 

 Silurian formations, and are at any rate in a highly inclined 



