564 GRKAT SERPENTINE-BKLT OF NEW SOUTH WALES, V., 



River seems to hide some line of faulting or discontinuity, in the 

 litholof^ical character of the countr3\ 



Igneous Rocks of the Middle Devonian Series. 

 In the foregoing, the more important occurrences of igneous 

 rock have been brietly mentioned, but no attempt has been made 

 to discuss the conditions attending their development. This we 

 will now endeavour to do. The most varied and instructive area 

 is that of East Gap Hill, of which a sketch map is given (Text- 

 tig.4). Passing from north to south, one has : — 



1. Massive dolerite. 



H.Porphyritic spilite. 



S.Spilite only slightly porphyritic. 



4. Vesicular spilite. 



5. Passage-rocks between vesicular spilite and V)reccia. 



6. Breccia or agglomerate. 

 There exists a very clearly marked boundary between the 

 first two, but a gradual passage between all the other menjbers. 

 There can be no doubt that the dolerite is intrusive into the 

 cherts, and also into the spilites. 'J he relations of the spilites 

 are not so clear. Along the eastern, and presumably lower 

 side of the igneous mass, the boundary of the spilite seems to 

 transgress the bedding of the cherts, and is rather irregular, 

 thougrh it is not clear whether it should be considered trans- 

 gressively intrusive into consolidated cherts, or merely into, the 

 semi-liquid unconsolidated sediments on the sea-floor. This 

 point was discussed in another connection in the previous 

 paper(17). The igneous rock along this eastern (lower) side is 

 locally brecciated, and such breccias, often with the relations of 

 intrusion-breccias, may contain very vesicular patches. These 

 vesicular patches of breccia may grade into massive vesicular 

 rock and thence into the dense solid rock of the main mass of 

 spilite. 'J'his seems to indicate that the igneous mass was 

 intruded into sediments that were at least partially consolidated. 

 From this edge of the mass, there projects a narrow tongue of 

 solid spilite a short distance to the east, but it is not clear that 

 this is a feeding dyke; it may be merely a portion of the mass 



