148 GREAT SERPENTINE BELT OP NEW SOUTH WALES, iv., 



incorporated in tiie crystallising moving melt, which chilled and 

 solidified rapidly. In other words, it is a flow-breccia. When 

 decomposed, this rock appears in handspecimen like a schistose 

 tuff. A thick band of it crosses the eastern branch of Munro's 

 Creek. 



The most peculiar rocks are the variolites. There are several 

 types of these. The most aphanitic stage is a dense, pale green 

 rock containing white spherical spots, which have no definite 

 outlines. It occurs in a narrow pillowy mass on the western- 

 most tributary of Munro's Creek, and again on the main creek 

 near the Razorback(l034, 1089). Under the microscope, it is 

 seen to possess a grey-green base divided up into acutely angular 

 portions separated by straight colourless rods running in all 

 directions(Pl.xxvi.,f.9). These rods are quite sharply bounded, but 

 their nature and composition cannot be determined. They suggest 

 felspar by their appearance, but are untwinned and divided into 

 irregular lengths, each occupied by a single transparent mineral, 

 different in optical orientation from its neighbours. The elonga- 

 tion of these short portions of the rods may be positive or nega- 

 tive. Professor Gregory has described similar structures in the 

 variolite of the Fichtelgebirge(18), and Michael Levy in that of 

 Durance(19).* These authors suggest that these maybe contrac- 

 tion-cracks filled with secondary felspathic material. The same 

 explanation may hold for the rocks under discussion, but it is 

 difficult to account for the absolute rectilinearity of the struc- 

 tures. Where these rods intersect, there are occasionally radiate 

 spherulites of felspar (varioles). The angular spaces between the 

 rods are composed of very fine green fibres, with a radial or 

 curved arrangement about one or more centres, often recalling 

 the arrangement of the line of force about a bar-magnet. They 

 lie in a colourless, weakly birefringent groundraass. The greenish 

 fibres extinguish at small angles, and are probably chlorite. No 

 primary minerals or recognisable pseudomorphs occur in these 

 rocks. In a more crystalline stage of this rock, the chlorite 

 plates are more individualised; large plates are associated with 



* For a summary of all the earlier work on variolites, see Gregory and 

 Cole's paper, " Variolitic Rocks of Monte Genevre," Quart. Jouni. Geol. 

 Soc, 1890. 



