Vol. 69.] PETROLOGY OF THE KALGOORLIE GOLDFIELD. 649 



in the same crystal, as if it were affected by the character of 

 the minerals undergoing replacement. A similar development of 

 large magnetite octahedra frequently accompanies the formation 

 of the carbonate rhombs, but is also noticed in rocks in which 

 the carbonates are not thus individualized. As both these minerals 

 occur in sharp and uncrushed crystals in highly-sheared rocks, their 

 formation appears to be posterior to the shearing. 



Schistosity in the greenstones is most pronounced in the vicinity 

 of the Golden Gate railway-station (at the north-western corner of 



Pig. 2. — ' Archipelago ' of quartz in quartz-cMerite-greenstone, 

 Ivanhoe O.M. x 30. 



[The quartz is in the position of extinction. The rest of the field 

 (not filled in) is occupied by a mixture of secondary minerals.] 



' The Mile '), where every gradation between a slightly-sheared 

 greenstone and a highly-fissile chlorite-schist may be observed. 

 In the intermediate types ' augen,' formed of archipelagos of quartz 

 and slightly-deformed leucoxene-crystals, are wrapped round by 

 parallel layers of chlorite and muscovite, interspersed with bands 

 of granular quartz. In the most schistose types the leucoxene 

 is drawn out into long lenticular streaks, and has been largely 

 replaced by rutile ; the larger ' augen ' of quartz have broken down, 

 and parallel layers of chlorite and subsidiary muscovite alternate 

 with layers consisting of a fine-grained mosaic of quartz, felspars, 

 and carbonates. 



There are many abnormal types of quartz-dolerite-greenstone, 

 both in the ' North End ' and in ' The Mile ' ; but, as their 



