46 



Rocks of Noyang. 



rare and slight traces of hydrated iron ore completed the 

 composition of this rock. 



(2.) This slice much resembled the last described, but in 

 the ground-mass of quartz and felspar I observed several 

 crystals of quartz of the kind so commonly found in these 

 porphyrites. There were also some porphyritic crystals of 

 felspar, which were so much kaolinised that all that can be 

 said of them is that they were plagioclase. Finally, there 

 were some slight traces of chlorite and much more hydrated 

 iron ore distributed through the whole rock than in the 

 other example. 



It was unfortunate that this sample was the one which I 

 selected for analysis, and which, being the more porphyritic, 

 and the more altered by decomposition, of the two,fwas 

 less well suited for the purpose I had intended. 



The rock when examined in a hand sample has a compact, 

 nearly milk-white appearance, with here and there slight 

 ferruginous stains, and a few small quartz-crystals can^be 

 made out. 



In the subjoined analysis the silica was not directly 

 determined. 



No. 6. QUARTZ-PORPHYRITE. 



. 10-3 



. 1- 





Per cent. 



Molecular 

 Proportions. 



Si0 2 



... 78-77 . 



.. 26-26 = 



A1 2 ° 3 



... 12-44 . 



. 2-43 ) 

 •12/- 



FeO 



... -95 . 



CaO 

 MgO 



•53 . 



•02 . 



. -19) 



. -oi ]- 



K 2 



•24 . 



•05) 

 . 2-19 } = 

 •29 j 



Na 2 



... 6-79 . 



H 2 



•26 . 





100-00 



31-54 



Hygroscopic moisture 



•14 



Specific 



gravity 



2-614 





Patio 



Si0 3 



... 26-26 



E 2 3 



.. 2-55 



= EO 



RoO 



•20 

 2-53 



■08 



The calculation of the mineral percentage may be made 

 as follows : — 



