233 



by a light brown gi-oiiiKhnass, bearing great resemblance to the 

 colour of chocolate, whilst that of the other specimen is yellowish 

 brown. Microscopically the groundmass is like that of the porphyry 

 from the Wai Husn microgranitic. The i)Orj)hyric crystals of quartz 

 are bluish and attain a diameter of 2 — 4 mm. The flesh-coloured 

 orthoclase crystals attain a length of about 1 cm. Microscopically 

 they are covered with a fine brown pigment and partly altered into 

 an aggregate of little muscovite-scales. The groundmass is micro- 

 granitic and consists of a fine aggregate of quartz and orthoclase. 



Sijenite-porplujry. Only one specimen of this I'ock originating from 

 the Wai Majo is present. With the uaked eye only a few dark 

 constituents can be detected in the grey to brownish dense ground-mass 

 showing a somewhat violet tint, with the help of the magnifying glass 

 likewise little rectangular sections of whitish grey feldspar can be 

 discovered. From the microscopic examination it appears that they 

 consist for the greater part of orthoclase, partly however also of 

 plagioclase (oligoclase). The dark constituents are in the first place 

 represented by green hornblende. The pleochroism is a =:: yellowish 

 green, b = dark green, c z= bluish green; c ]> l^ ^ a ; c:i = \2°. 

 Besides this biotite occurred frequently, which was however completely 

 transformed into chlorite, whilst grains of ore and epidote were 

 formed. Apatite is found in the shape of little thick prisms. The 

 groundmass is entirely crystalline and is composed of aggregates of 

 particles of feldspar, among which a few little, angular grains of 

 quartz occur. 



From the scarcity of porphyric rocks in Taliabu may be deduced 

 that originally they occurred oidy in the form of dikes. 



Diabase. This kind of rock is likewise only represented by one 

 specimen from the boulders of the Wai Kabuta. It is dull, greenish- 

 grey and contains a few macroscopically observable dull-white 

 crystals of feldspar. In thin sections the characteristic ophitic structure 

 is to be observed, narrow and broader lath-shaped crystals of plagio- 

 clase, between which the xenomorphic augites appear, which have 

 undergone however partly an alteration into epidote. Grains of black 

 ore are freely dispersed. On the fissures of the rock greenish-yellow 

 epidotes have deposited themselves, which are accompanied by quartz. 



The oldest sediments found in Taliabu are represented — in so 

 far as it is known — by p/ii/Uiies, which have submitted to a very 

 strong folding, as was already remarked by van Nouhuys at the place 

 mentioned. An extensive I'egion is watered by the Wai Miha, i.e. 

 from its source till it leaves the chasm between the Bapen Kudi and 

 Bono Kedotó, whereupon it reappears again at Nali. In some spots 



