604 GREAT SERPEXTINE-BELT OF NEW SOUTH WALES_, V., 



The pyroclastic rocks of the Igneous Zone on East Gap Hill 

 extend down to Portion 138, and near their southern extremity, in 

 Portion 110, is the fragmental magnetite-keratophyre mentioned 

 above (1122). It, also, is possibly a flow-breccia. It is extremely 

 patchy in constitution ; adjacent portions are of different composi- 

 tion and texture ; and the types of texture seen are usually different 

 from those which are present in the magnetite-keratophyre-breccias 

 at Hyde's Creek, near Bowling- Alley Point. The groundmass of 

 the rock is very like a sponge. The "sponge"-fabric is made up of 

 fine laths of albite, clouded by kaolin, etc., and so darkened with 

 abundant masses of minutely divided magnetite, that it is almost 

 opaque. The interstices are filled with minute prisms of glassy 

 albite, generally twinned, and accompanied by a little chlorite. Set 

 in this matrix, are fragments of dense trachytic magnetite-kerato- 

 phyre, with phenoerysts of albite and sometimes of fresh augite, 

 and, in addition, there are fragments of normal trachytic kerato- 

 phyre, with very little magnetite or augite. These inclusions vary 

 from very minutely to coarsely crystalline types, and the latter 

 may even be sufficiently rich in augite, to be classed as dolerites 

 (Plate lii., fig. 4). A large vesicle present in the rock has been 

 filled by a spongy mixture of albite and calcite. There can be little 

 doubt that this rock has been affected by pneumatolytic solutions, 

 which introduced the sodic felspar. The abundance of haematite, 

 which gives the dominant red colour to the ferruginous pryoclastic 

 rocks at the southern end of East Gap Hill, is probably also due to 

 the action of these solutions, which have oxidised the magnetite in 

 the magnetite-keratophyres. In those ferruginous keratophyres 

 in which the iron ore seems to be of secondary, pneumatolytic 

 origin, it is possible that the ore was deposited in the rock, in part 

 at least, as hsematite. In those, however, in which the majority of 

 the iron occurs as magnetite, the dark grey colour is the character- 

 istic feature. Of these. Specimen 1178 is typical. It has some 

 macroseopical resemblance to 1122, but has very little groundmass. 

 It consists of fragments of keratophyre, of which twelve different 

 samples are to be found in a slice scarcely two square centimetres 

 in area. These are closely fitted together, with a little cement made 



