BY W. N. BENSON. 587 



tourmaline, are to be found near the Kootiugal railway-station, 

 and a beautiful garnetiferous, and graphic tourmaline-aplite, is 

 developed on the travelling stock-route, in the north-eastern corner 

 of the Parish of Tamworth. Dykes of finely granular rocks of 

 intermediate composition are found, and are best described as 

 microdiorite and micromonzonites, or diorite and monzonite 

 aplites; and a peculiar lamprophyre, which has the mineralogical 

 composition of an augite-minette, and contains spherulites of 

 quartz and felspar. A few dykes of pegmatite and quartz-por- 

 phry extend from the granite into the surrounding Devonian rocks, 

 but only for a short distance. This absence of an extensive series 

 of dyke-rocks is a characteristic feature of the Moonbi granite. 



The metamorphosing effect produced by the granite on the sur- 

 rounding rocks has been considerable, and is especially noteworthy 

 in the limestones, and the pyroclastic rocks. In the latter, it gener- 

 ally has the effect of causing the augite to change into the stable 

 actinolite, rather than into chlorite, the ilmenite is replaced by 

 sphene, and the felspar is recrystallised, sometimes as a mosaic of 

 minute, indeterminable, untwinned grains, and sometimes in clear 

 crystals of andesine. In the more altered types, abundant tiny 

 plates of biotite are formed, the calcite in the vesicles, or irregu- 

 larly distributed throughout the rock, passes into garnet, and, 

 still more rarely, some secondary pyroxene is , developed at the 

 expense of the amphibole. These rocks are best developed in a rail- 

 way cutting east of Tintinhull, while the most altered garnetiferous 

 types occur in Portions 113, 123, and 169, Parish of Nemingha. 

 Rocks with secondary pyroxene also occur in the north-eastern 

 corner of the Parish of Tamworth. Associated with the garneti- 

 ferous rocks in Nemingha, are massive hornblende-schists, repre- 

 senting former dolerites, and garnetiferous hornblende-schists, that 

 were, in all probability, amygdaloidal spilites. The hornblende- 

 schists, which extend southwards from Portion 157, and those 

 occurring in Portions 42, 63, and 64, Nemingha, are probably 

 also altered spilites. The zone of alteration of the igneous rocks 

 varies somewhat in width; generally, it is about a quarter of a 

 mile across. 



