126 GREAT SERPENTINE BELT OF NEW SOUTH WALES, iv., 



veins occur in the vicinity. Owing to the abundance of porphyry 

 dykes in the vicinity, it was thought probable that the boric 

 acid may have been derived from an underlying mass of granite 

 which approached the surface in this region, though none of the 

 porphyries contain tourmaline. There is, however, the possibility 

 that the axinite may proceed from the dolerite-magma itself : 

 axinitic contact-rocks are occasionally observed about diabases 

 in Germany and New JerseydS). 



On Tom Tiger, the prominent peak north of the junction of 

 Swamp Creek and the Peel River, pillow-structure is to be seen 

 in the crags about the summit. The pillows are sometimes more 

 than a yard in diameter, and their marginal zones of chilling are 

 narrow and not well marked. They are separated by narrow 

 bands of epidote, calcite and quartz. No exposures of the contact- 

 line between the sediments and the igneous rock can be seen on 

 Tom Tiger itself, but in Swamp Creek, half a mile to the south, 

 a strongly intrusive junction is exposed. The bared rocks in 

 the creek-bottom show that a considerable thickness, about ten 

 yards, of fairly coarse-grained spilite is full of irregular, twisted 

 fragments of chert of all sizes. The whole appearance suggests 

 that the igneous rock invaded partially consolidated sediments. 

 Pillow-structure is also observable here. Following the zone 

 further southwards, pillow-structure is again met with on the 

 ridge separating Swamp Creek and Happy Valley, and from this 

 was obtained the specimen of spilite, of which an analysis was 

 given in Part iii. The map in Part ii. shows a break in the 

 spilite-zone south of this point, but it has now been proved to 

 extend uninterruptedly to beyond Oakenville Creek, and the 

 contacts with the sedimentary rocks, wherever visible, show the 

 intrusive nature of the igneous rock. 



A thickness of over four hundred feet of pillow-lava is exposed 

 in the bed of Happy Valley. The pillows vary from a few inches 

 to over six feet in diameter; the inner portion is porphyritic, 

 with a subvariolitic base; the outer and rapidly chilled portions 

 are aphanitic, and have frequently a variolitic structure. Vesicles 

 are not abundant, nor are they concentrically arranged; they 

 tend to concentrate towards the centres of the pillows. The 



