18 



Notes on the Diabase Rocks 



markably fresh and unaltered. The porphyritic felspars 

 were of the description which I have already given, and 

 very clear and fresh ; the principal thing to be noted being 

 the deposit of ferric oxide in translucent red patches in the 

 fractures and cleavages. The augite was colourless in short, 

 stout crystals. It also occurred as clusters of irregular 

 crystals, and I also observed grains included in plagioclase 

 felspars. This augite was more or less converted into 

 calcite; enstatite was numerous, as previously described, and 

 almost the whole of it was converted into bastite (serpen- 

 tine). Iron ores were precisely as mentioned before. The 

 ground-mass consisted as usual of very numerous micro- 

 scopic prisms of apparently triclinic felspars, of magnetite 

 grains, and some basis, together with minute trichites and 

 brown spherulitic bodies. In addition to the above, there 

 were in all the slices, but more in some than in others, 

 cavities filled by agate. 



The analysis was carried out mainly by the ammonium 

 fluoride process, FeO was determined by the bichromate 

 process, and the alkalis by Smith's method; Si0 2 — P 2 5 , 

 CO 2, and H 2 S0 4 were specially determined. As neither 

 Ti0 2 nor MnO were met with in the course of analysis, I 

 made special examinations confirming their absence. The 

 specific gravity of the sample was taken by means of 

 Walker's steelyard balance. 





Per cent. 



Molecules. 



Katio. 





Si0 2 



... 53-39 



177.Q8 /Acids, less) 

 - u <™\ freeSi0 2 f = 



3-822 



Al 2 3 



Fe 2 3 



... 15-23 

 ... 873 



... 29-57 t 

 ... 10-91 J 



K 2 3 = 



1-000 



FeO 



... 3-61 



... 10-03 ) 







CaO 



.. 8-46 



... 30-20 5- 



no = 



1-503 



MgO 



.. 412 



... 20-60 ) 







K 2 



1-84 



392 ) 







Na 2 



.. 3-60 



... 11-61 > 



R 2 



•696 



H 2 



.. 1-14 



12-66 ) 







co 2 



•22 



1-00 







p 2 °. 



•16 



•23 



Proportion of Acids) - , 

 to Bases J 







100-50 



94 to 1 







(Indicative Ratio). 





Hygroscop 



ic moisture 



... -60 







Pyrite ... 



... 



... -16 







Specific gr 



a vity 



... 2-814 







