30 Mr. J. A. Phillips on the Composition and Origin of 



I. II. 



Water* 1*20 1*26 



Silica 74-62 74*76 



Alumina .... 16*29 16*13 



Ferrous oxide . . . 1*18 1*15 



Ferric oxide . . . trace trace 



Manganous oxide . . *55 *62 



Lime *30 *26 



Magnesia .... *50 *46 



Potassa 3*54 3*74 



Soda 1*24 1*13 



Lithia *11 *09 



9^53 99*60 



A microscopical examination of this rock does not afford 

 much information not to be obtained by a close inspection of 

 hand-specimens. A large proportion of the felspar is seen to 

 be monoclinic ; but triclinic felspar is also present in considerable 

 quantity. The outlines of the crystals are not in all cases 

 sharply defined, and they are sometimes rendered slightly cloudy 

 by some nocculent chloritic mineral. Two varieties of mica are 

 distinctly visible, and occur in both quartz and felspar, together 

 with a little tourmaline. The quartz is much fissured, the sides 

 of the cracks being apparently coated by ferric oxide • it con- 

 tains numerous fluid-cavities enclosing bubbles, which in some 

 of the smaller ones are observed to be in constant motion. 



Clay-slate fyc. — In those portions of the mine situated at a 

 distance from the cross-course, the " killas " is a very hard clay- 

 slate of a grey colour. Cleavage is in the majority of cases to 

 some extent obliterated; no trace of crystalline structure can be 

 detected ; and the rock, in addition to being traversed by nume- 

 rous strings of white quartz, is thickly studded with minute 

 spots and crystals of iron pyrites. Sp. gr. =2*73. 



In the immediate vicinity of the fault, which appears to fur- 

 nish a channel for the passage of the saline waters, the slate has 

 become much altered, is of a dark green colour, consists to a 

 great extent of minute acicular crystals, with their longer axes 

 parallel to the planes of cleavage, and in many cases closely re- 

 sembles some varieties of serpentine. Crystals of chlorite are 

 found in the joints of cleavage. It also exhibits many of those 

 highly polished surfaces so frequently met with in serpenti- 

 nous rocks. Sp. gr. =2*69. 



By analysis these rocks were respectively found to have the 

 following compositions : — 



* Of which "34 was lost in the water-bath. 



