Rocks of Noyang. 



41 



Both the felspar crystals and the quartz I found to be 

 surrounded by a margin of crypto-crystalline ground-mass, 

 which gradually passed into the micro -crystalline-granular 

 structure of the major part of the slice. 



(3.) A few small chlorite pseudomorphs after magnesia-iron- 

 mica are scattered through the ground -mass. The character 

 of this mineral is precisely that already described. 



This rock, therefore, clearly has been a quartz-mica- 

 porphyrite, in which the porphyritic characters are only 

 slightly marked, and in which the RO minerals are almost 

 absent. It nearly represents the ground-mass of such a rock 

 as that already described as typical of this group. 



The following analysis and calculation of the mineral per- 

 centage is of a sample of this dyke : — 



No. 5. QUARTZ-MICA-PORPHYRITE, 



Molecular 

 Proportions. 



Per cent 



Ratio. 



p 2 o 5 



Si0 2 



A1 2 3 



Fe 2 3 



FeO 



CaO 



MgO 



K a O 



Na 2 



HO 



tr. 



77-66 



12-30 



•61 



•17 



•16 



•73 



•19 



6-96 



•46 



25-89 = Si0 2 

 •08 f ~ K * U 3 



... 25-89 . 

 ... 2-47 . 



.. 10-5 

 .. 1- 



•05) 



•06 V = RO 

 •36 ) 

 •04) 

 2-25 V= R„0 

 ■51 J 



... -47 . 



... 2-80' . 



.. -2 

 .. 1-1 



99-24 

 Hygroscopic moisture 

 Specific gravity 



31-63 

 •33 

 2-634 



The following may be taken as the probable composition 

 of this rock calculated into its component minerals: — 



