BY W. N BENSON. 669 



long rows of axiolites, with a central string of minute magnetite 

 grains. Here and there, the flow-lines diverge around some pheno- 

 eryst of orthoclase, or spherulitic patch, or quartz-area free from 

 flow-structure (Plate xxv., fig. 5). The glassy rocks have similar 

 quartz and felspar phenocrysts, set in a ground-mass which may 

 be purely glassy, with a definite flow-band on a rippling structure, 

 or may be more or less homogeneous. This is usually devitrified, to 

 a greater or less extent. In one interesting rock [M.B., 7], the 

 phenocrysts, quartz, oligoclase, biotite, hornblende, and magnetite, 

 are greater in amount than the glassy matrix in which they are 

 imbedded. 



In the last rock, the felspar is nearly all plagioclase, but, in the 

 majority of the rocks, orthoclase is abundant. This point is im- 

 portant, as it would show this series of rocks to be normally potas- 

 sic lavas, not sodic keratophyres ; and, therefore, not part of the 

 spilite-keratophyre group, as instituted by Messrs. Dewey and 

 Flett. The lavas, here described, have not been chemically investi- 

 gated, but they are almost certainly comagmatic with the Carboni- 

 ferous rhyolites of the Maitland District, described by Walkom 

 and Browne(13), which are normally potassic, as may be seen from 

 Mr. Mingaye's analysis. Walkom and Browne's analysis of a pitch- 

 stone, from the same region, would, however, show that sodic rocks 

 are also present. 



A rock [M.B.,233] occurs in Jerry's Creek, four miles south of 

 Crow Mountain, which may possibly be connected with this 

 series. It consists of xenocrysts of plagioclase and augite, which 

 have been rolled about in a cooling lava. The rock has a regu- 

 larly slaggy structure, and bent microlites of felspar throng its 

 brown, glassy ground-mass (Plate xxv., fig.6). 



(5). Peridotites and associated Rocks. — The ultrabasic rocks 

 are fairly constant throughout the whole length of the serpentine- 

 belt. As shown by Mr. Andersond), the dominant rock was a 

 harzbergite, but locally, by diminution in the amount of enstatite, 

 the rock approaches to the dunites, while the presence of diallage 

 throws the rock into the Iherzolites. Diminution or absence of 

 olivine gives an enstatite-rock, " Enstatolite " of Pratt and 

 Lewis(35). 



