130 Fotes on the Area of Intrusive Rocks at Dargo. 



No. 1. — Argillite. 



Ti.O,, 



•49 



si.o; 



51-33 



Al.,0.. 



25-69 



Fe. 



4-80 



Fe.O 



107 



Ca.O 



•25 



Mff.O 



2-72 



K,0 



6^13 



Na.,0 



•77 



H.6 



6-73* 





99-98 



Moisture 



1-53 



Sp.gr 



2-686 



In the absence of more knowledge of the nature of the 

 minerals which form this rock, any attempt to calculate out 

 the percentages would be purely hypothetical, and the con- 

 stituent minerals are so minute that their isolation seems 

 more than difficult. All that can be said from the examina- 

 tion which I have detailed is that the rock appears to be 

 composed almost altogether of two minerals, one of which 

 is probably a potassa-mica, and the other may belong to the 

 chlorite group. The rock seems to be an example of those 

 paleozoic sediments which, as I mentioned in a former paper, 

 have undergone only the preliminary stage of meta- 

 morphism. 



2. Sandstone. — The second example represents the sand- 

 stones of the locality. It is grey in colour, and very much 

 indurated. Traces of the bedding remain where small 

 argillaceous fragments are imbedded in the same plane. 



Under the microscope I found a thin slice of this rock to 

 be composed of angular grains of quartz in large amount, 

 angular fragments of felspar, mostly orthoclase, of the 

 character of that found in granitic rocks, others of micro- 

 cline, finally a few fragments of triclinic felspars, either oligo- 

 clase or albite. The interstitial material is plentiful, and has 

 been converted into mica_, which is mostly in aggregates of 

 minute scales, but with a few larger flakes, which have all 

 the appearance of muscovite. 



* Including graphite. 



