594 GREAT SERPENTINE-BELT OF NEW SOUTH WALES, V., 



l(jneous Mocks in the Middle Devonian Series. 



These rocks include many types of dolerite, spilite, and kerato- 

 pliyre, and the pyroclastic rocks, as well as the metamorphosed 

 equivalents of these. 



The dolerites differ from one another in texture, the composition 

 of the felspar, and the nature of the pyroxene. The quartz-doler- 

 ite, which forms a very small mass in Portion 110, Nemingha 

 (1132), is characterised by the presence of basic andesine or 

 labradorite as the dominant mineral, as is also that which occurs 

 near the magnetite-keratophyre in Portion 175,(1107, 1128), and 

 that which invades the porphyritic spilite on the northern end of 

 East Gap Hill (see Text-fig. 4). These rocks have a granitoid 

 texture, the felspar-prismoids, being approximately idiomorphic, 

 and often strongly zoned. The augite is of the normal character, 

 slightly decomposed, and possessing a large optic axial angle. 

 Quartz occurs in large grains, or in granophyric intergrowth with 

 felspar. Ilmenite is abundant, and apatite rare, though some large 

 prisms occur. The chemical composition of 1132 is given on page 

 74a ; the composition of the felspar calculated from this would be 

 Or-Ab4 7An4 9, or, reckoning orthoclase as albitejAbg.^An^y, 

 which corresponds with the result of the optical determination. 

 The dolerite on the north of East Gap Hill contains some highly 

 granophyric masses, while there is also some uralitised albitic 

 dolerite, from Portion 204, Nemingha, which cannot be distin- 

 guished macroscopically from the adjacent calcic variety. 



The porphyrite, which occurs in Portion 158, Woolomol(1162), 

 is rather different from these. This is so free from any sign of 

 eontact-metamorphism, though within the zone of altered rocks, 

 that some doubt must remain, as to whether it is really coeval with 

 the Devonian doleritic series. It is, however, quite unlike any 

 Tertiary basic rock known to the writer. It has a fine-grained base, 

 consisting of prismoids of andesine, with chlorite replacing augite, 

 titanomagnetite, a very little quartz and apatite. The phenocrysts 

 are sometimes as much as 3 mm. in diameter. They consist of 

 plagioclase, with zones of liquid inclusions, and have commenced 



