( 39è ) 



Petrography. - "The mineralogie and chemical composition of some 

 rucks from Central Borneo". By J. Schmutzer. (Communicated 



by Prut'. A. Wk iim \nn). j ) 



(Communicated in the meeting, of October 31, 1908). 



Prof. M. Dittrich ai Heidelberg analized the following four rocks, 

 collected by Prol', (i. A. V. Molengraaff in Central Borneo: 



11 710, a glassy amphiboledacite, round as a boulder on a boulder- 

 bank in the Soengei Sëbilit, ± 3 KM. above Kebijau. *). 



II 599, the glassy amphiboledacite of which consist the rocks, 

 1.50 in. high, in the Soengei Embahoe, below Nangah 

 Pi inali : the hand-specimen was struck close to he con- 

 tact with the adjacent rock (silicifie tuffbreccia). s ) 



11 7411, biotiteamphiboleandesite with old habitus from the righl 

 bank of the Soengei Tëbaoeng over againsi Nangah Oeroei. 4 ). 



I <s ( .):>, aplitic microgranite from the waterfall, N.W. cliff, Boekit 

 kehun. 6 ) 



I. Hyalopilitic . hnphiboletlaciti { Amphibolephyrivitroyellowstonose). 



The grey-black, glassy rock shows a rough, conchoidal fracture ; 

 only very indistinctly n few while feldspar-phenocrysts, whose diameter 

 «Iocs not exceed 1 nun., and veiy rare, bright glittering, stiil smaller 

 green amphibole-needles appear forth from the greasy-shining ground- 

 mass. Under the miscroscope the plagioclase of the first generation 

 (andesine-oligoclase) forms sharp idiomorphic crystals, lying mostly 

 isolated, but sometimes combining into aggregates. Zonal structure 

 is locally finely developed; among the twin-laws the albite-law reigns; 

 the Carlsbad- and pericline-law occur only subordinately. Here and 

 there the feldspar shows a pronounced inclination to forming skeleton 



'i The Dutch communication was entitled ''The mineralogie and chemical com- 

 posilion of some rocks from the Miiller-Mountains in Central-Borneo". I avail myself 

 of this opportunity to repair a lapsus calami, only tin 1 three first rocks described 

 originating from die Müller-Mpuntains, Mt. Kelam not forming part of this range. 



~i cf. Molengraaff, Geological Explorations in Gential Borneo, Leyden 1902, 

 L'O'.t, where this rock is named pitchstore. 



R ) The label bears the indication "' , Km. below Nangah Pëmali", whilst ac- 

 cording to Molengraaff's description, op. cit. -l\'ü . and the map Vlllb, published 

 by him at the same lime, this should rather be about 100 meters. Tnere can he 

 no doubt, however, about the identity of the rock meant by him in his work I.e., 

 with that described here, as the nick builds up the first dyke of andesite in the 

 tuffbreccia below Nangah Pëmali. 



') .Mi. Loeboek enusists of die same rock, ibid. l!93 - 295. 



•m ibid. 127 Chapi. VI), 138. 



