36 Notes on the Diabase Rocks 



The microscopic examination of this rock shows all the 

 characteristic features of a quartz felsite, and I think that 

 the most reasonable conclusion to arrive at is, that it repre- 

 sents a " lava flow " contemporaneous with the formation of 

 those felsitic beds which occupy the same relative position 

 to the limestones elsewhere, that this quartz felsite does at 

 the place described. The numerous embedded fragments 

 must in this case be regarded as having been taken up by the 

 fluid lava. The full relations of this rock to the associated 

 fragmental beds can only be ascertained by a more minute 

 examination of the intervening parts of the Murendel valley 

 than I could as yet make. I must, however, point out that 

 I have observed and described a case at the Buchan River, 

 near Mount Dawson, where I could distinctly trace the 

 passage of a fragmental felsitic bed into completely com- 

 pacted rocks, exactly resembling a quartz felsite in outward 

 appearance. In that case I could not feel any doubt that the 

 felsitic material had been regenerated by means of some form 

 of metamorphism as a rock simulating a quartz felsite. In 

 this present case, however, I cannot either feel any doubt 

 that the rock I have just described is a true eruptive 

 rock. 



The Buchan beds, as I have here and elsewhere described 

 them, rest as a whole upon a vast thickness of the still older 

 Snowy River porphyries. These, which occupy at least an 

 area of 500 square miles, are composed of felsitic rocks, such 

 as massive quartz felsites (quartz porphjaies) of a granitoid, 

 or of a compact, or, in places, even a vesicular, character. A 

 veiy large proportion consists of fragmental beds either more 

 or less bedded, or being agglomerates, not only of the above 

 felsitic rocks, but also of older sediments (silurian), or even 

 of granite. The fragments are of all sizes, from dust up to 

 many tons in weight. Felsite dykes are a feature in many 

 places traversing them. The thickness of the Snowy River 

 porphyries is not evident, as they extend from the summit 

 of the table-land of Woolgulmerang, where they are best seen, 

 down to the very water-level of the Snowy River, where 

 the sections terminate — a depth of some 2000 feet. 



The Snowy River porphyries are to all appearance 

 younger than the Upper Silurian, and they are certainly older 

 than the Middle Devonian Buchan beds which rest upon 

 them. It is possible that they may represent the Lower De- 

 vonian formations which have hitherto not been recognised in 

 Victoria. If so, it would probably have been a period of 



