Geology. — "On the Age of the fgneous Rocks in the Moluccas'. 

 By Prof. H. A. Brouwer. (Commiiiiicatecl by Prof. G. A. F. 

 Molengra.aff). 



(Communicated in the meeting of Jan. 27, 1917). 



In Verbkek's ') latest geological iiieinöir o\\ the Moluccas, eruptive 

 rocks have been classified as follows : 



1. old basic igneous rocks mostly of pre-perniian age (azoic and 

 palaeozoic). Some may possibly be mesozoic. Petrographically are 

 distinguished neridotite, serpentine, gabbro, diabase porphyrite with 

 their tuffs and breccias, diorite and diorite-porphyrite, the last two 

 of minor significance, etc. 



2. granitic rocks probably all of pre-pennian age. 



3. old-meso-volcanic igneons rocks. Older melaphyres, qnarlz- 

 porphyries and qiiartz-porphyrites, probably also some diabases and 

 diabase porphyrites. Verbeek points out that no conclusive evidence 

 has as yet been adduced to establish the age of the rocks classed 

 among this group; he also surmises that pai't of them still belongs 

 to the permian formation. 



4. young-meso-volcanic igneous rocks (cretaceous), andesites, dacites 

 and acid melaphyres with bronzite. Perhaps they belong partly to 

 the old-meso-volcanic igneous rocks, another part niay be even of 

 old-tertiary age. 



5. tertiary igneous rocks nowhere seem to go back to the eocene, 

 because the nummulitic limestones are entirely devoid of debris of 

 andesites, with which miocene sediments abound. 



a. leucite- and nepheline rocks (old miocene or younger) considered 

 to be the oldest group on account of the structure of the volcano 

 Lurns in Java with an older rim of leucite basalt and a younger 

 cone of hornblende-andesite. 



h. old hornblende-andesites and biotite andesites with their tuffs 

 and breccias (miocene). They have an individual existence, rarely 

 do they constitute the base or the oldest rim of the large volcanoes 

 of which some are still active. The latter cannot be separated from 



•) R. D, M. Verbeek. Molukken Verslag. Jaarb v. h. Mijnwezen 1908. Wetensch. 

 Ged. p. 737 seqq. (Rapport sur les Moluques). 



