102 Supplementary Notes on the Diabase Rocks 



the ground-mass becomes coarser in its elements, and the 

 basis disappears. 



In the ground-mass there are numerous fragments of 

 quartz crystals, but these are " eroded," as is so frequently 

 the case with quartz crystals in rocks of the quartz 

 porphyry or quartz porphyrite classes, as, for instance, in 

 those I have lately described from Noyang.* 



I observed in some slices more than in others porphyritic 

 felspars, as well as quartz crystals. These felspars have 

 been so much altered that it is difficult to speak with abso- 

 lute certainty as to what some of them have been. Some 

 are converted into a- saussurite-like compound, others are 

 kaolinised and infiltrated by iron ore ; but after a careful 

 examination and comparison I have come to the conclusion 

 that the majority of these porphyritic felspars were plagio- 

 clase. 



I have not observed either mica or hornblende. The 

 general red colour of these rocks is due to their being per- 

 meated by ferric hydrate, which is a secondary product. 



According to the above definitions these rocks belong to 

 the quartz p or phy rites. 



Somewhat to the north of the high point marked (h) in 

 the diagram section, I have found an outcrop of rocks in 

 one of the gullies leading to the Murendel Eiver. The 

 samples which I collected prove upon examination to belong 

 to this section of my description. They are harsh textured 

 rocks of a dark colour, inclining to grey or olive. They dip 

 S. 10° W. at about 15°, and they appear to be bedded lavas, 

 for I observed in them very numerous vesicles drawn out 

 in a direction not quite that of the dip, indicating move- 

 ments in the rocks when they took up their present 

 positions. I found by the examination of thin slices that 

 this rock has a ground-mass composed of quartz and felspar 

 in variable proportions. In one part of a slice I also 

 observed a mass of brown glassy basis enclosing portions of 

 the micro-crystalline granular materials. 



In this ground-mass there are very numerous quartz 

 crystals, one of which is eroded and filled in by it 

 in the characteristic manner. I found also several por- 

 phyritic crystals of felspar, in some of which I could observe 

 the twin structure of the triclinic felspars. As a rule, 

 these felspars are too much altered for their original 



* Royal Society of Victoria, read 10th May, 1883. 



