BY W. N. BENSON. 699 



granular plagioclase, with abundant, small crystals of apatite 

 (Plate xxvii., Fig. 15). 



(11) The alkaline rocks of the Nandewar Mountains have been 

 described in detail by Dr. JensenO). He considers them to be of 

 Eocene age, and he determined the occurrence of the following 

 types :— 



Volcanic — alkaline rhyolite, trachytes, phonolites, alkaline ande- 

 sites, and basalts. 



Hypabyssal — alkaline syenite-porphyry, pulaskite-porphyry, 

 augite-porphyrites and teschenites, monchiquitic lamprophyres. 



(12a) The Tertiary basalts are of several varieties. In general, 

 they are normal, fine-grained olivine-basalts, quite noncrystalline 

 and undecomposed. In other places, they are hypocrystalline, and, 

 east of Hanging Rock, some layers of very decomposed basalt- 

 scoria have been discovered. There are also more coarsely grained 

 and porphyritic types. For convenience, we will describe the 

 Nundle and Barraba basalts separately, as they present somewhat 

 different features, and are possibly not of the same age. 



The following rocks are the most typical of those developed in 

 the northern district. M.B., 75, which occurs four miles east of 

 Barraba, and forms portion of the Bell's Mountain flow, is a 

 medium-grained, holocrystalline rock, with well developed ophitic 

 structure, consisting of laths of andesine, faintly purple augite, 

 small olivine-grains, well formed ilmenite-plates, long apatite- 

 needles, and a few minute flakes of biotite. M.B., 193, occurred in 

 Chain of Ponds Creek, eight miles north-west of Barraba. It was 

 not in situ. It is a fine-grained rock, with a pilotaxitic texture, 

 composed of labradorite-laths, olivine, granular augite, platy ilmen- 

 ite, and apatite-needles. In this matrix are large, clear crystals of 

 bytownite, free from schiller-plates, and considerably corroded. 

 Here and there, felspar has been secondarily deposited on the pre- 

 viously corroded surface. These large crystals are not zoned, and 

 are probably xenocrysts, though it is not impossible that they 

 should have been derived from the magma by an intratelluric crys- 



