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



cites the researches of Lenarcic(32), and Day and Allen(33) on the 

 lowering of the viscosity produced by the presence of a small 

 amount of magnetite in an albite-melt, and notes that the 

 eutectic albite-magnetite ratio of three to one, as determined by 

 Doelter(34), seems to be a frequent one in the magnetite-syenite- 

 porphyries. At the same time, he recognises the presence of a 

 certain amount of pneumatolytic action, affirming that the ores 

 stand in pegmatitic relation to the parent-magma, there being 

 evidence for thjs presence of a considerable amount of magmatic 

 water. (Apatite occurs with the ores.) His view differs from 

 that of Stutzer chiefly in the advocation of an effusive, not in- 

 trusive, origin for the syenite- porphyries. 



The most significant features of our rocks seem to l)e the fol- 

 lowing : they solidified from a magma under non-uniform pressure, 

 and hence are not only strongly trachytic, but were broken up 

 as they solidified, and the keratophyres now consist of closely 

 compacted, minute fragments of trachytic rock, usually without 

 any matrix, occasionally with a matrix of non-trachytic acid 

 keratophyre, a consolidation of the residual magma under static 

 conditions. Most of the fragments have preserved the straight 

 direction of the flow-structure, some have been bent, some have 

 been actually rolled up into a concentric arrangement, and this 

 is most frequent when the fragment has a kernel of magnetite- 

 bearing rock. The magnetite-keratophyre forms the central 

 portion of the keratophyre-mass; around it is a zone of parti- 

 coloured nodular or breccia-like mixtures of magnetite-kerato- 

 phyre with purely albitic rock. In these, the distribution of 

 the magnetite is most irregular, but, in the main, it is suggestive 

 of the occurrence of two periods of crystallisation. It rarely, if 

 ever, occurs as inclusions in the crystals of felspar, but lies in 

 an extremely divided state between the felspar-laths. Part of 

 it is segregated into nodules of rounded or irregular shape, some- 

 times broken across by the brecci«,tion, and here showing a sharp 

 fractured boundary, but more usually without any sharp bound- 

 ary, passing out into the albitic rock, which may have a con- 

 tinuous rectilinear flow-direction, or may bend to more or less 

 encircle the dark portion. This seems to show that the presence 



