23^ 



their statements were a short time ago confirmed bv W. Voltz'). On 

 the contrary J. Ahlburg writes: '-Was das Verhalten der Gesteine 

 "[der Tinombotbrmation] znm Granit betrifï't, so ist es immerhin von 

 "Bedeutung, dass wohl nahezu alle echten Granite des Indischen 

 "Archipels, vor allem die Granite von Malakka, Sumatra, 

 "nnd Bangka, ebenso die grosse Granitplatte von Südwestborneo, 

 "palaozoischen nnd zwar in den meisten Fallen nachwei.slich '') kar- 

 "bonischen Alters sind." ^) 



Mr. Ahlburg is prudent enougli not to mention the names of his 

 informants. 



Granite-porphyry. Hitherto this rock has only been found as erratic 

 rock, namely by \l. D. M. Verbekk on the north coast, near Cape 

 Damar '), by G. Boehm in the Wai Kadai (described by H. Bucking') 

 and by J. W. van Nouhuys in the Wai Ha, a tributary of the Wai 

 Miha. The granite-porphyry of the latter linding-place contains a 

 yellowish brown, line crystalline groundmass, in which numerous 

 grains and dihexaedrons of quartz are inclosed. The light-yellowish 

 crystals of orthoclase — sometimes twins according to the law of 

 Karlsbad — are dull and ha\e caused the formation of scaly mus- 

 covite, as appears fi'om the microscopic examination. They are 

 moreover filled up with finely distril)uted brown iron ore. The much 

 less numerous twinned individuals of plagioclase have caused a 

 similar alteration as the orthoclase. The crystals of quartz are 

 characterized by numerous finid-inclusions. Sometimes the intrusion 

 of the groundmass is perceived, but glassy inclosures are utterly 

 wanting. Dark constituents were only exceptionally found, and if so, 

 in an entirely decomposed condition. The previous occurrence of 

 biotite however is unmistakable, as the shapes of the laminae are 

 found back in the limonite into which they liave changed. The 

 feldspars which form a part of the groundmass as w^ell as tlie 

 porphyric crystals have caused a transformation into musco\ite. 



Quartz-porp]iyry was collected by G. Boehm in the Wai Husu 

 and examined by H. Bltking. In Van Nouhuys's collection are 

 two specimens from the boulders of the Wai Najo. One is characterized 



1) Oberer Jura in West-Sumatra. Cenlralbl. f. Min. 1918, p. 757. — Siid-China 

 und Nord-Sumatra. Milleiluugen des Ferd. v. Richtbofen-Tages 1913. Berlin 1914, 

 p. 37. 



-) The italics are mine. 



3) Versucli einer geologischen Dar-jlellung der Insel Celebes. (Geolog. und 

 palaeonlologische Abh.dlg. von J. F. Pompecki und Fr. Von Huexe, N. F. 12. 

 Jena 1913, p. 28). 



*) Molukken-Verslag, p. 223. 



"J G. Boehm. Neues aus dem ludo-Auslralischen Archipel, p. 391. 



