BY L. A. COTTON. 



833 



the composition of the zones varying from albite-oligoclase at the 

 margin, to basic plagioclase in the centre of the crystals. 



The augite, which is slightly more coloured than that of the 

 Oakey Creek dolerite, is much less abundant than in that rock. 

 The grains, moreover, are much smaller in size. 



The chlorite, which is also less abundant than in the Oakey 

 Creek dolerite, has the same characteristic relation to the felspars, 

 and, moreover, the same strange property of including idiomorphic 

 quartz-crystals. These quartz-crystals are, however, less abundant 

 in this rock. The same problem as to the origin of the chlorite, 

 therefore, exists. 



Ilmenite is more abundant than in the Oakey Creek dolerite, 

 as also is leucoxene. 



Analyses and Molecular Ratios. 

 i. Oakey Creek quartz-dolerite. 

 ii. Staggy Creek quartz-dolerite. 



ill. Hard rock (blue ground) De Beer's Mine, Kiinberley. 

 iA. Molecular ratios of i. 

 iiA. Molecular ratios of ii. 



