322 



colour is dark brown to greenish-yellow. The pleochroism 

 is intense, showing practically complete absorption. The 

 biotite encloses such minerals of earlier formation as apatite, 

 zircon, and ilmenite. 



Chlorite and epidote are developed as secondary pro- 

 ducts. The small amount of muscovite occurs in association 

 with the biotite, and is of later crystallization. It remains 

 clear and unaltered. 



Apatite occurs in slender needles and small hexagonal 

 prisms. It is most abundant as inclusions in the biotite. 



Ilmenite is associated with the biotite, and is generally 

 surrounded by a white leucoxenic decomposition product. 



Zircon, like apatite, is enclosed in biotite, and occurs 

 in short prisms. It is usually surrounded by faint pleochroic 

 haloes. 



Epidote is present, associated with biotite and plagio- 

 clase; it probably results from the interaction of biotite 

 and plagioclase, and is obviously of secondary origin. Calcite 

 may be developed in addition. 



Kaolin occurs as a dust accompanying both felspars. 



The cores of some sections of the plagioclase show plen- 

 tiful sericite, occurring in small flakes, sometimes to the 

 complete exclusion of the felspar, from which it has developed. 

 It is probably paragonitic in composition. 



The order of crystallization of the constituent minerals 

 may be subdivided as : — 



I. Accessories — Apatite, ilmenite, zircon. 

 II. Biotite and accessory muscovite. 



III. Plagioclase — Quartz and microcline. 

 Overlapping of the crystallization periods of II. and III. 

 occurred, as is evidenced by inclusions. This particularly 

 refers to microcline, which in its occasional porphyritic deve- 

 lopment is then referable to an early stage. The order of 

 cessation of crystallization is more truly represented by the 

 above arrangement. 



Nearing the completion of crystallization, the sodic 

 character of the plagioclase had become marked, in some 

 sections oligoclase-albite being developed independently, and 

 the last stages are represented by the graphic intergrowths 

 of quartz and microcline which surround the larger crystals. 



The relative proportions of plagioclase to microcline 

 felspar show some variation in the different sections ex- 

 amined. As a whole they are present in approximately equal 

 amounts. The granite may therefore be placed in the 

 Adamellite group. 



Cognate Xenoliths. — These occur as ellipsoidal or ovoid 

 patches in the main granite. In hand specimens they appear 



