66 Rocks of Noyang. 



67°, and is traversed by two systems of well-marked joints, 

 one dipping N 60° E at 30°, and the other S 55° E at 42°, 

 and these are so marked that it requires an examination of 

 the texture of the rock to determine that they are joints, and 

 not bedding planes. 



The metamorphism of the sediments continues for 

 several miles down the valley of the Tambo River, showing 

 the neighbourhood of the intrusive rocks, which then re- 

 appear in a somewhat peculiar form as a crystalline-granular 

 compound of quartz and felspar, almost wholly devoid of 

 mica or hornblende. The composition of these rocks is that 

 which, under favourable circumstances, might have consoli- 

 dated as a quartz-porphyrite, such as are seen near Noyang. 



I prepared some slices of these rocks, and I found them, 

 as their appearance in the field had indicated, to be composed 

 essentially of felspar and quartz, with very slight traces of 

 a brown magnesia-iron-mica. The felspars were of three 

 kinds : one highly compounded according to the combined 

 Albite and Carlsbad laws, and with small angles formed by 

 the plane of vibration with the composition face, in one 

 case so small as almost to coincide with the twin plane. The 

 second felspar was evidently orthoclase, and was kaolinised. 

 The third felspar was microcline. A little chloritic mineral 

 is distributed through the whole rock. 



The quartz in this sample fills in large spaces, and is 

 remarkable for the numerous microliths it contains. Many 

 of these are of some chlorite mineral, some are ores of iron, 

 and some have even the appearance of felspar fragments. 

 Fluid cavities were not numerous. 



Another sample which I collected at a further distance I 

 found to be less quartzose, more felspathic, and to be also 

 entirely free from mica. The felspars were in large tabular 

 crystals, which had slightly interfered with each other's 

 growth. The best crystallised appeared to be oligoclase, and 

 •the least well-formed were microcline. 



V. — Conclusion. 



The age of the Noyang intrusive rocks must remain some- 

 what uncertain. All that can be stated with any degree of 

 certainty is that they are younger than the goldfields series 

 of North Gippsland, and therefore probably younger than 

 Lower Silurian. The geological structure of the district, 



