694 GREAT SERPENTINE BELT OP NEW SOUTH WALES, iii., 



strain-effect, biotite (slightly chloritised, with haloed zircon-inclu- 

 sions), twinned hornblende sometimes idiomorphic, well crystal- 

 lised magnetite, and apatite, together with a little secondary epi- 

 dote. This may clearly be classed as a granodiorite. N.T., 413, 

 will fall into the same group, though it differs in its smaller grain- 

 size, greater amount of orthoclase, absence of hornblende, rarity of 

 magnetite, and presence of a little sphene. The grain-size is less 

 regular, and the orthoclase occurs in a few large grains poikiliti- 

 cally enclosing quartz and plagioclase. 



Of the apophyses, the most striking are the black felspar-por- 

 phyries, or malchites. These are very abundant, especially east of 

 Munro's Creek. They have a dark, aphanitic ground-mass, with 

 white phenocrysts of plagioclase, and sometimes smaller, dark 

 phenocrysts of hornblende. Microscopically, the rocks are seen to 

 consist of idiomorphic prisms of brown hornblende, with usually 

 small, fibrous extensions of actinolite, as described by Cross. The 

 felspar is also idiomorphic; it is zoned and twinned on the albite, 

 pericline, carlsbad, and (rarely) manebach laws; its average com- 

 position varies from acid labradorite to basic oligoclase. It is often 

 much decomposed, with formation of zoisite, sericite, etc. The 

 ground-mass is exceedingly fine-grained, consisting of lathy or 

 granular plagioclase crowded with very minute, but perfect horn- 

 blende-prisms. Some magnetite is present in the phenocrysts and 

 ground-mass. Sometimes a little biotite is present. In N.T., 89, is 

 a large, chloritising flake encircled by small hornblende-prisms. 

 This interesting specimen shows also a contact-surface with the 

 spilites and the edge of the epidote-veins in these basic rocks. A 

 vein in the spilite stops short at the boundary of the porphyry. 

 Along the surface of contact, there is a zone only 2 mm. thick, 

 crowded with phenocrysts with general flow-direction. In places, 

 a small vein of quartz appears in the actual line of contact (Plate 

 xxvii., Fig. 13). 



Sometimes these porphyries are entirely decomposed {e.g., N.T., 

 62), and are then dense, cream-coloured rocks, in which the origi- 

 nal hornblende is represented by limonite-pseudomorphs. 



