Notes on the Area of Intrusive Rocks at Dargo. 137 

 No. 3. — Aplite. 



76-48 



13-94 



tr. 



1-08 



•01 



4-90 



3-70 



•86 



100-97 



•15 



2-611 



Al.,03 

 Fe.,03 



Ca.O 

 Mg.O 

 H O 

 Na.,0 

 H,0 



Moisture 

 Sp.gr..-. 



Disreofarclino: a small amount of kaolin and of masfnesia- 

 mica, the above analysis calculates out satisfactorily for a rock 

 composed of orthoclase, felspar, oligoclase, and quartz. The 

 oligoclase is of the composition of ab. 6, an. 1, and therefore 

 very near to the border of the group nearest to albite.* 

 The orthoclase, oligoclase, and quartz are in almost equal 

 molecular proportions. 



Besides these dykes, which are characteristic of the con- 

 tacts, there are also numerous other dykes, many of which 

 traverse the intrusive masses, and perhaps more frequently 

 than the adjoining schists. It is, however, possible that this 

 may be more in appearance than in reality, owing to such 

 dykes being more easily seen in the former than in the latter 

 country. 



I selected three samples of dykes as being typical of those 

 which I had met with. 



* There is some little difference in the views expressed by authorities 

 as to the limits of the albite and oligoclase groups, as will be seen from the 

 following particulars, extracted from works at hand : — 



Albite. Oligoclase. 



Eosenbusch ... Ab 1 an to ab 8 an 1 ... Ab 6 an 1 to ab 2 an 1 

 Tschermak ... Ab ... Ab to ab 3 an 1 



Lapparent ... Ab ... Ab 3 an 1 



] Ire classe ... ... Ab 3 an 1 to ab 5 an 1 



Des Cloizeaux > 2de classe ... ... Ab 4 an 1 to ab 2 an 1 



) 3me classe ... ... ab 2 an 1 



Eosenbusch — Physiographic, &c., 2nd edition, Vol. I., p. 521. 

 Tschermak— Mineralogie, 2nd edition, p. 465. 

 Lapparent — Cours de Mineralogie, 1884, p. 350. 

 Des Cloizeaux, Oligoclase and Andesine, Tours, p. 9. 



