122 GREAT SERPENTINE BELT OP NEW SOUTH WALES, iv,, 



exists in the nomenclature. It was pointed out that the term 

 " spilite " by original definition and present-day usage covered 

 only such rocks as had undergone a considerable amount of 

 alteration, with the formation of abundant secondary minerals. 

 This has not always been the case among our rocks in New South 

 Wales, unless we are to consider the acid felspar as a secondary 

 mineral (a point which is discussed below), though in all essential 

 features, chemical composition, structural characteristics, and 

 geological association, they agree entirely with the rocks to which 

 Dr. Flett has applied the term "spilite." To indicate this 

 similarity in essential features, it seemed best to extend the use 

 of the term to cover the apparently unaltered rocks in New South 

 Wales, and the name " spilite " will be employed in the sequel in 

 the same sense as before. The distinction adopted to separate 

 the dolerites and spilites, is one of texture and grainsize: the 

 former have a coarse or medium grainsize, with an ophitic, granu- 

 lar, or intersertal texture; the latter are fine-grained, or partially 

 glassy, with a more or less variolitic texture. All gradations 

 may be found between them. Mineralogically, they differ from 

 normal dolerites and basalts chiefly in the strongly sodic nature 

 of their felspars. 



Geological Occurrence. — The general sequence of sedimentation 

 in the Nundle district has been already discussed in Part ii. of 

 this series. Briefly, the Devonian formation consists of a lower 

 portion, the Woolomin Series, comprising phyllites, tuffs, and 

 radiolarian jasper; a middle portion, the Bowling Alley or Tam- 

 worth Series, consisting of radiolarian cherts and claystones, 

 volcanic tuffs and breccias, and coral limestones; and an upper 

 portion, the Nundle or Barraba Series, made up of mudstones, 

 containing Lepidodendron australe and radiolaria, with numerous 

 bands of tuff and breccia. Spilites and dolerites occur in some 

 amount in the Woolomin Series, are abundant in the Bowling 

 Alley Series, but are absent from the Nundle Series In Car- 

 boniferous times, the formation was strongly folded, and slightly 

 overturned towards the west, and a great mass of peridotite was 

 injected into the plane separating the Woolomin Series from the 

 main bulk of the Bowling Alley Series. A large amount of 



