38 



Rocks of JS r oyang. 



leaving the ragged-edged cavity usual in such cases. The 

 ground-mass of felspar and quartz granules was wholly un- 

 attacked. 



The result, therefore, of this test has been to show that if 

 any difference exists in the power of resistance against altera- 

 tion between the porphyritic felspars and the felspar granules 

 of the ground-mass, it is in favour of the latter. We have 

 another instance of the rule that the earlier consolidated 

 felspars are the more basic. 



The following is an analysis of this rock : — 



No. 4. QlJARTZ-MlCA-PORPHYRITE. 





Per cent. 



Molecular 

 Proportions. 



Katio. 





P 2 °5 



tr 









SiOo 



. 72-39 . 



. 24-13 Si0 o 



... 24-13 . 



. 8-4 



Al o 3 . 

 Fe;0 3 .. 



. 14-42 . 

 . -56 . 



: % 8 ?K° 3 



... 2.87 . 



. 1- 



FeO 



•30 . 



•08 \ 







MnO 

 CaO 



•01 . 



. -85 . 



: *o\*° 



... 1-31 . 



•4 



MgO 



, 1-85 . 



•93 j 







K 2 



. 1-23 . 



•26) 







Na 2 . 



. 5-93 . 



. 1-91 VR 2 



... 3-42 . 



. 1-2 



H 2 . 



.. 1-13 . 



98-67 



. 1-25) 

 31-73 







Hygroscopi 



c moisture 



•55 







Specific gvi 



i vity 



2-632 







Taking the microscopic examination as the basis, the 

 above may be calculated into mineral percentages as 

 follows : — 



