214 KEY. J. MILNE CUKRAN. 



the slice is reduced to the required thinness, the rock appears of 

 a blood-red colour. As far as I can make out, it is a perfect glass, 

 there being no individualized matter in any of the slices I have 

 prepared. As these rocks are almost as interesting in hand-speci- 

 mens as in thin slices, I have preserved a few chips for inspection. 

 The Carcoar basalt-glass will be found numbered " 200 " and the 

 Battery Hill and Hill End specimens " 202 " and " 201 " respec- 

 tively. A thick polished slice of the Vegetable Creek rock is 

 numbered " 203." 



Slices 85 and 85b. — Magma Basalt from Gulgong, New South 

 Wales. This interesting rock was collected by Mr. M. Orlivich 

 about ten miles north of Gulgong. It has the general appearance 

 of a basalt-glass in hand specimens, but crystals of pyroxene are 

 visible to the unaided eye. Under the microscope, this rock is 

 seen to consist of brown glass, in which are imbeded crystals of a 

 monoclinic pyroxene. The glass contains considerable quantities 

 of those needle-shaped bodies that are often seen both in the glass 

 and felspars of basalt, but their exact nature is not known. They 

 are most plentiful in slices which show patches of clear glass. 

 There is very little of this in Slice 85, but instead there is a 

 remarkable development of large rods which cross and cover the 

 field in confused masses. Some of these rods are sensibly pleo- 

 chroic. They are, without doubt, incipient crystal aggregations. 

 Incipient crystals are also to be seen in faint lines, having other 

 lines branching to the left and right at right angles. A most 

 interesting skeleton crystal of augite is also present on this slice. 



Slice 60. — Hornblende Biotite Granite from Bathurst, New 

 South Wales. In hand-specimens, this rock shows all its min- 

 erals to the unaided eye. Prisms of hornblende are common, 

 measuring one-eighth of an inch along the vertical axis. Nests 

 of biotite are also clearly visible. These two minerals scattered 

 through the customary complements of quartz and felspar give the 

 rock, at a distance, a light grey colour, with just a shade of blue. 

 Occasional twins of orthoclase may be discovered by reflected light. 

 Thin flakes of biotite can be detached and show all the optical 



