BY W. N. BENSON. 701 



main basalt shows a cooling rim of more dense crystallisation about 

 such inclusions. The fluidal basalts have a smooth weathering sur- 

 face, break with a more regular fracture, and atmospheric cor- 

 rosion etches out the flow-lines as they twist round xenocrysts, or 

 pass regularly through the rock [N.T., 174]. Microscopically, 

 these are distinctly fluidal, the felspar-laths have a general direc- 

 tion, the magnetite and augite of the base are very minute indeed, 

 while the olivine-crystals are larger. They are decomposing into 

 bowlingite. Fluxional structure is also seen in the bending of the 

 rock, in zones of slightly different grain-size, and the enrichment 

 of some zones in magnetite. There are small inclusions of coarse- 

 grained rock, chiefly composed of felspar-laths and ilmenite, while 

 large xenocrysts of olivine are visible in hand-specimens. 



Other normal basalts occur, without this granular or fluidal 

 structure, and, in them, the usual nodules of olivine-enstatite and 

 picotite occur, together with large grains of pleonasteC?) nearly 

 half an inch in diameter. 



Associated with these basalts are some dolerites very rich in 

 chlorite, occurring south and east of Sheba Mountain. As an 

 example, N.T., 171, may be described. It is subophitic in texture, 

 with medium grain-size. About half the augite is replaced by a 

 yellow-green aggregate of chlorite-spherulites, surrounded by a 

 double layer of chlorite, the inner, green, the outer, brown. These 

 consist of minute fibres standing perpendicularly to the enclosing 

 and included laths of felspar. The augite is purplish, and there 

 are a few pseudomorphs after olivine. Ilmenite and apatite occur 

 in small amount. Other rocks differ in the presence of one chlorite 

 layer only. 



The interesting alkaline rocks of the Nundle district, and similar 

 rocks in the Mount Royal Range, have been already described by 

 the present writer, and reasons have been given for considering 

 that they occur as sills in the Tertiary basalt(H). A few more 

 particulars may now be given. 



The rock capping Square Top Hill, three miles west of Nundle, 

 is dark grey in hand-specimens, with purple-brown augites, and, 



