326 



there are present a few scattered grains of blue strongly 

 pleochroic tourmaline. The albite in this rock is more 

 abundant than in the aplite described above. 



The specific gravities of the rocks of this series are 

 indicated below: — 



(%.) Fine-grained red aplite, D 1 J = 2'590. 

 (ii-J Medium-grained red aplite, D 2 Jo = 2"602. 



(Hi. J Coarse-grained red aplite, D 1 ^° = 2'605. 

 (iv.J Aplite from near Pink Bay, D 1 £o = 2'625. 



The aplites of this series are characterized by the pre- 

 dominance of microcline felspar; plagioclase is subordinate. 

 This plagioclase is an acid albite, and in the finer-grained 

 aplite may appear as idiomorphic phenocrysts rarely, the 

 main development being in association with the quartz and 

 mircrocline. The listed specific gravities further point to 

 the dominant felspar being potassic. A partial analysis of 

 the fine-grained red aplite yielded K 2 = 5*48%, Na 3 = 2"79%. 



The pink colour of this series is due to the presence of 

 a fine film of haematite dusting; the cleavages and cracks of 

 the alkali felspars. 



IV. Products of Pxeumatolysis of the Pink Aplite. 



These may be listed as follows: — (a J The quartz-tour- 

 maline nodules (Pneumatoliths) ; (h) the greisen : (c) the 

 kaolin. 



The quartz-tourmaline nodules have already been 

 described in the paper cited above. They were developed 

 anteriorly to the greisen, which will now be discussed. 



(b) The Greisen. — Subsequent to the consolidation of the 

 aplite fissures in turn were developed and afforded an avenue 

 of escape for the remaining volatile constituents, now much 

 reduced in temperature. 



The effects of the volatile constituents are denoted by 

 the presence of quartz veins and the occurrence of small quan- 

 tities of greisen developed as an alteration of the aplite. 



The quartz of the vein material has crystallized in the 

 characteristic prismatic crystals capped with pyramid faces. 

 A section across a quartz vein to the original aplite shows 

 in succession-quartz, an alteration product of the aplite which 

 proves to be a greisen, and this grades into an unaltered 

 aplite. 



In hand specimens the greisen has a porous, fine-grained, 

 light-greenish appearance, and with the aid of a lens quartz 

 and a lightish-green mica are easily recognized. The porous 

 character of the rock is well marked. 



