700 GREAT SERPENTINE BELT OF NEW SOUTH WALES, iii., 



tallisation. M.B., 341, which covers the auriferous gravels of Tea- 

 Tree Gully, is a fine-grained rock, with small olivine-crystals visible 

 in hand-specimen. It consists of idiomorphic laths of basic labra- 

 dorite, olivine, and numerous smaller grains of augite. There is a 

 considerable amount of dark groundmass, which contains, in a 

 glassy base, microlites and skeleton-crystals of felspar, augite- 

 needles, and abundant, minute plates of ilmenite standing perpen- 

 dicularly to the crystal-surfaces of the earlier-formed crystals and 

 the microlites. As noticed by Mr. Card, in his description of the 

 basalts overlying the diatomaceous earths near Chain of Ponds 

 Creek(32a) } all these basalts are remarkably fresh, a fact support- 

 ing their comparatively recent extrusion. 



The basaltic neck in the Hall's Creek Valley, near Bingara 

 ("Ruby Hill"), has been described petrologically by Mr. Card(45), 

 from specimens collected by Mr. Pittman. He drew attention to 

 the occurrence, in it, of an eclogite, with kelyphitically bordered 

 garnet, and omphacite which was included in the basalt, either in 

 fragments of rock (xenoliths), or in isolated xenocrysts. The 

 basalt rises up, in dykes, through a breccia, with fragments and 

 xenocrysts from the same rock. 



The basalts of the Nundle region are also varied. The fine- 

 grained rocks may be divided into two types, the granular, and the 

 fluidal. The granular rocks have a rough surface on weathering, 

 and break with a hackly fracture, appearing to be an aggregate of 

 pellets of basalt, rather than a simple rock. Some rocks can be 

 divided into granular masses of the size of small peas, e.g., N.T., 

 160, which occurs on the Yerrowinn-flow, one mile west of the sum- 

 mit. Microscopically, this rock shows no sign of such a structure ; 

 it is a normal, fine-grained rock, consisting of very small felspar- 

 laths, augite-prisms, magnetite-cubes and octahedra, and larger 

 crystals of olivine, decomposing with the formation of limonite. 

 Here and there are inclusions of a rather more coarsely-grained, 

 ophitic basalt, in which the olivine is in tiny, ovoid grains. The 



*Rec. Geol. Surv. N.S.W. 1897, Vol. v., Part 3, p.20. 



