Rocks of Noyang. 51 



making a quantitative analysis, as it seemed that no results of 

 value would be likely to be attained. 



The mode of occurrence of these black and vitreous rocks 

 entirely among the crystalline-granular and porphyritic 

 members of the series suggests that they represent the 

 plug of a vent which emitted a lava that included numerous 

 extraneous fragments, partly derived from below and partly 

 from the volcanic dust which had fallen back again into 

 the orifice. The fact that it is from this locality that the 

 quartz-porphyrite dykes and dyke-like masses radiate, 

 lends strength to such a supposition. 



(e.) Diorites. 



Traversing the quartz-mica diorites and porphyrites, but 

 not so far as I know in connection with the later igneous 

 rocks, there are numerous dykes which are all marked by a 

 dark greenish colour and a finely crystalline structure. 

 They are good examples of rocks which were formerly all 

 classed as " greenstones," and which, as dykes, are very com- 

 mon in the Gippsland mountains. There is little in their 

 occurrence to show whether they do or do not belong to the 

 series of rocks which I have now described ; but they 

 certainly do appear to be more plentiful in the area of 

 igneous rocks than outside of it ; and I have observed the 

 same fact elsewhere ; for instance, at Swift's Creek, where 

 dykes of very basic character, being mainly amphibole, 

 traverse the quartz-diorites, and are, I think, connected with 

 the intrusive areas of amphibole rocks (Schillerstein) which 

 are the youngest of all the series which, together collectively,, 

 constitute the intrusive area at that place. An instance of 

 these dykes occurs at Navigation Creek, in the quartz- 

 mica-diorites. It is about thirty inches in width, and strikes 

 N 55° W. The rock in mass has a dark greenish colour, and 

 weathers with a rough exterior ; a fresh surface shows a 

 minutely crystalline structure, and here and there a few small 

 grains of pyrite. Under the microscope, in a thin slice, I 

 found it to be composed as under — 



(1.) Felspars which form a network — or, perhaps, more 

 properly, groups — in which several crystals are in juxta- 

 position with others at various angles. They are much 

 eroded, and more or less filled by alteration products ; and of 

 these epidote in granular masses, and of a pale yellow colour, 



