234 



the rock contains strata aiul lenses of qnariz and occasionally much 

 pjrile ^). A second region that has not been thoronghl}- expioi'ed is 

 found, according to the map, at (he npper course of Wai Kabuta. 



Besides the finding-places mentioned above, van Nouhuys mentions 

 the river Langsa, but he remarks emphatically that the phjllites 

 occur there ou\y in boulders, but nowhere ^) in the form of rocks. One 

 of the specimens is composed of alternating thin, dark-coloured, 

 almost black strata, and lighter brownish-grey strata more rich in 

 quartz. From the microscopic examination it appears that biotite 

 forms the chief constituent, occasionally accompanied by many grains 

 of ore and fine black particles of dust and only few prisms of tour- 

 maline and grains of titanite. The lighter strata consist chiefly of 

 an aggregate of qnartz grains among which are numerous little biotite- 

 laminae. The rock is moreover penetrated in several directions by 

 small veins of quartz, in which yellowish-green, wormshaped aggre- 

 gates of little pleochroitical laminae of chloi-ite (helminth). 



Another phyllite is of a blackish-grey colour, dense and rather 

 hard. In consequence of the decomposition of the rock such parts 

 as are richer in quartz appear at the surface as knots. Microscopic- 

 ally the little biotite-lamellae are irregularly spread over the quartz-mass, 

 and sometimes closely compressed in accumulations. Sometimes a light 



Fie. 2. 



1) Bijdrage tot de kennis van het eiland Taliabii, pp. 958, 961, 1174—1176, 

 1187—1188. 

 ~) Page 1180. 



